TREATISE 



ON 



THE STEAM ENGINE. 



BY 



JAMES RENWICK, LL.D. 

PROFESSOR OF NATURAL AND EXPERIMENTAL PHILOSOPHY AND CHEMISTRY, 
IN COLUMBIA COLLEGE, NEW-YORK. 



SECOND EDITION, 



REVISED AND ENLARGED 







NEW- YORK : 
CARVILL & CO. 

SUCCESSORS TO G. & C. CARVILL &. CO. 
NO. 108 BROADWAY. 

1839. 






Tsi 4.(04- 






"5 



Entered according to the Act of Congress, in the year 1839, by 

CARVILL & CO. 

in the Clerk's Office of the District Court of the Southern District of New-York. 




t 



% 



V 



New- York: 

Printed by Scatchkrd & Adams, 

No. 38 Gold Street. 



PREFACE- 



The second edition of the " Treatise on the Steam 
Engine/' has been carefully revised, and many parts 
of it have been either re-written or much extended. 
Since the publication of the first edition, great im- 
provements have taken place in the manner of using 
steam, and in two of its most important applications. 
The expansive action of steam, which was employed 
only in a few boats on the Hudson, has received a de- 
velopment in practice fully equal to what the author 
had anticipated, while the value of this mode action 
has been illustrated by the publication of its results in 
the pumping engines of Cornwall. The views of the 
author in respect to the defects of the existing theory 
of the motion of steam vessels have been confirmed, 
and new illustrations, derived from actual experiment, 
have been given in their proper place. The naviga- 
tion of the ocean by steam, the practicability of which 
was denied by many, has been proved to be safe and 
certain. Finally, the use of steam in locomotion, 
which in 1830 was little more than in embryo, has 
been much extended and improved. The additions 

E 



IV PREFACE. 

which have been made to the work have reference 
chiefly to these important subjects. For much valu- 
able information in respect to steam navigation, ac- 
knowledgment is due to Mr. Haswell, the engineer of 
the U. S. Ship Fulton. 

Although the imperfection of the theories of Robiscn 
and Tredgold has long been apparent, it has not 
been thought proper to abandon them altogether. It 
was, however, in contemplation to have attempted an 
exposition of a theory more consistent with true me- 
chanical principles. This attempt has been render- 
ed unnecessary by the successful investigations of Pam- 
bour, which are inserted in the form of an Appendix. 
It is still thought too early, in a work intended for prac- 
tical men, to take this theory as the basis of our in- 
ference. The mode of proceeding in the former edi- 
tion has in consequence not been altered. 

Columbia College. ) 
1st June, 1839. j 



PREFACE 



TO THE FIRST EDITION. 



The Treatise which is now submitted to the public 
does not pretend to the merit of originality. Ali that 
has been attempted is to exhibit in a succinct, and, as 
far as possible, popular form, the present state of our 
knowledge on the interesting subject of which it treats. 
From this the sole exceotions are the theories of the 
expansive action of the steam engine, and of steam- 
boats. To the former has been added the considera- 
tion of the physical circumstances that were left out 
of view in the investigations of Watt and Robison ; 
and the latter has been examined upon principles that, 
so far as the author is aware, although of frequent ap- 
plication in other branches of practical machines, 
have never been taken into account in this particular 
case. 

Preparing the -work for the American public, and 
as a substitute for treatises either too expensive or too 
rare to be of frequent occurrence, the author has not 
scrupled to avail himself of the labours of his European 
predecessors. The authors that have been most fre- 
quently consulted, are : Peclet, from whose Traite de 
Chalsur much valuable matter has been drawn ; Farey 
and Tredsold ; while the researches of Stuart have 



TI PREFACE. 

"been of great service in the compilation of the histo- 
rical parts. 

The author has also derived much information 
from the friendly aid he has received in various ways 
from the most eminent manufacturers of the steam 
engine who were within his reach. To the West 
Point Foundry Association, to Mr. Allaire, and Mr. 
Sabbaton, of New- York, and to Messrs. Rush and 
Muhlenburg of Philadelphia, he takes this opportunity 
to return his acknowledgments for the liberal manner 
in which their practical knowledge has been laid open 
to him. 

To Captain Bunker, of the steam-boat President, 
and to Mr. R. L. Stevens, he has also been under ob- 
ligation for the facts in relation to steam-boats which 
he has adduced as the test of his theory. 

From Dr. McNiven he has received important facts 
in relation to the preliminary experiments of Fulton at 
Paris, and the first trial of his boat on the Hudson, at 
both of which that gentleman had the good fortune to 
be present. Had not the work been extended beyond 
the size originally intended, this communication would 
have been inserted entire in the Appendix. 

Should the present work be successful in extending 
the knowledge of the principles and mode of action of 
the most important of the instruments by which the 
power of man is extended ; and particularly, should it 
have an influence of bringing into use those precau- 
tions and apparatus by which the risk to which hu- 
man life is exposed, may be lessened, the object of 
the author will be fully accomplished. 

Columbia College. 
New- York, 3lth August. 



CONTENTS. 



CHAPTER L 



MECHANICAL AND PHYSICAL PRINCIPLES THAT ARE APPLICABLE TO THE CON- 
STRUCTION OF THE STEAM ENGINE- 

Page 
Division of Material substances. — Forces which determine the state in 
which they exist. — Forms which all bodies are capable of assuming. — Dif- 
ference in the mode of action of solids and fluids.— -Forces and Motion. 
Centres of Gravity, Inertia, Percussion, Oscillation, and Gyration. — Mo- 
tions found in natural agents, and in the parts of Machines. — Mechani- 
cal properties of fluids,— -Specific Gravities — Pressure of the Atmosphere 
and Barometer. — Heat and its effects. — Thermometer. — Expansion of 
bodies by heat. — Specific Heat. — Latent Heat. — Evaporation. — Radia- 
tion of Heat. — Conducting Power of bodies.— Mode in which liquids 
carry off heat. Cooling effect of gases. — Distribution of Heat among the 
particles of a solid. 31 

CHAPTER 1L 

COMBUSTION. 

Definition of Combustion. — Oxygen. — Flame. — Atmospheric Air. — Currents 
of Air produced by Combustion. — Increase of Weight in the process of 
Combustion.— Temperature of Flame, and modes of burning of Solids, 
Gases, and Liquids. — Different species of Fuel.— Properties and chemi- 
cal nature of Fuel. — Carbon and Hydrogen. — Comparative value of 
different kinds of Fuel. — Parts of Furnaces. — Ashpit. — Grate. — Body of 
the Furnace.— Flues.— Chimneys. — Damper. — Furnace doors. 32 

CHAPTER III. 

EOiLERS. 

Materials of which boilers are constructed. — Figure of Boilers. — Strength 
and thickness of Boilers. — Apparatus for showing the level of the water. 
—Feeding Apparatus.— Proof of Boilers. — Safety Valves. — Air Valves. — 



Vt CONTENTS. 

Page. 

Steam Guages.— Self-regulating Damper.— Common Damper and Register. 
— Dangers arising from the fire-surface becoming bare of water.— Ther- 
mometer. — Plates of fusible metal.— Valves opening at the limit of temper- 
ature.— Deposits of solid matter, and modes of lessening and removing them. 
— Steam-pipes. — Generator of Perkins. 53 

CHAPTER IV. 

GENERAL VIEW OF THE DOUBLE-ACTING CONDENSING ENGINE. 

Of Prime Movers in general.— Principles of the action of Machines.— 
Modes of applying Steam as a prime-mover. — Application of Steam to the 
Double-Acting Condensing Engine.— Modes of removing Water of 
Condensation and Vapour.— Modes of changing the reciprocating Rectili- 
neal Motion of the Piston- Rod into a reciprocating circular motion. — Me- 
thod of changing the reciprocating circular motion into a continuous one. 
Mode of regulating the varying motion of the Engine, and making it pro- 
duce one with uniform velocity. — Other methods of obtaining a rotary 
motion.— Effect of the joint action of two Engines — Water used to pro- 
duce condensation. Water that has been employed in condensation ap- 
plied to feed the boiler. — Manner ot ascertaining the state of the Vacuum 
formed by condensation.— Mode of regulating the supply of Steam. — Ac- 
cumulation of Steam in the boiler, and mode of preventing it. — Double- 
acting condensing Engine considered as self-acting.— Packing and Ce- 
ments. — Estimate of the power of the double-acting Condensing Engine. 
— Estimate of the quantity of water evaporated for each unit of force. — 
Estimate of the supply of water for the boiler. 97 

CHAPTER V. 

DESCRIPTION OF THE DOUBLE-ACTING CONDENSING ENGINE. 

Usual form of Double-Acting Condensing Engine. — Steam-pipe. — Jacket. 
— Side Pipes. — Slide Valve. — Puppet Valve. — Cylinder. — Cylinder Lid- 
— Cylinder Bottom. — Piston. — Woolf's Piston .— C art Wright's Metallic 
Packing. — Condenser. — Air Pumps. — Delivering door. — Air pump Buck- 
et.— Hot Water Cistern and Pump. — Cold Water Cistern. — Injection 
Cock. — Water of Condensation. — Cold Water Pump. — Parallel Motion. 
— Lever Beam. — Pump Rods: — Connecting Rod. — Crank. — Fly Wheel. 
— Tumbling Shaft. — Eccentric. — Double Eccentric. — Adjustment of Ec- 
centric—Governor. — Throttle Valve. — Other forms of Double-Acting 
Condensing Engine. — Mode of setting these Engines in motion. 12-1 

CHAPTER VI. 

GENERAL VIEW OF CONENSING ENGINF.S ACTING EXPANSIVELY, OF HIGH-PRES- 
SURE, SINGLE-ACTING, AND ATMOSPHERIC ENGINES, PARTICULAR DESCRIPTION 
OF HIGH PRESSURE ENGINES. 

Regulation of steam by the valves of Condensing Engines. — Expansive force 
of steam, supposing the temperature to remain constant. — Expansive force 



CONTENTS. Vll 

Page. 
of steam of a given tension and in a given engine, on the same hypothe- 
sis. — Expansive action of steam of a given tension and constant tempera- 
ture, when the friction and resistance are taken into view. — Expansive ac- 
tion at increasing tensions, and with temperatures varying according to the 
law of specific heat. — Effects of steam acting expansively, as usually em- 
ployed. — Action of high pressure steam when not condensed. — Cases in 
which high pressure engines are useful. — Reconsideration of the precau- 
tions to be used in boilers generating high steam.— General view of the 
high pressure engine, its steam pipes, side pipes, and valves. — Calculation 
of the power of high pressure engines, their working beam, parallel motion, 
throttle valve, governor, and forcing pump. — General view of the single- 
acting condensing atmospheric engines. — Particular description of a high 
pressure engine, with a beam, and of long and short slide valves. — Particu- 
lar description of a horizontal high pressure engine. 149 

CHAPTER VII. 

EARLY HISTORY OF THK STEAM ENGINE. 

Introduction. — Statue of Memnon. — Hero of Alexandria — Eolipyle. — Anthe- 
mius and Zeno. — Cardan. — Mathesius. — Baptista de Porta.— De Causs. 
— Brancas. — Wilkins and Kircher. — Marquis of Worcester. — Hautefeuille 
— Papin's first plan. — Savary.— Papin's Engine for the Elector of Hesse. — 
Newcomen and Cawley. — Potter's Sccggan. — Beighton's Hand-Gear. — 
Sineatou. — Leupold. 176 

CHAPTER VIII. 

CONCLUSION OF THE HISTORY OF THE STEAM ENGINE. 

Power and Defects of Newcomen's Engine.— Birth and education of Watt. 
— Professor Robison. Watt's first experiment. — Professor Anderson. — 
Watt's second Experiment. — Inferences. — Separate Condenser. — Steam 
applied as the moving power. — Packing. — Jacket and Air Pump. — Work- 
ing Model. — Dr. Roebuck. — Experimental Engine. — Watt's first patent. — 
Gainsborough's claim. — Boring apparatus. — Form of Watt's first Engine. 
Saving of Fuel. — Projects for rotary motion. — Fitzgerald, Stewart, and 
Clark. — Double-acting Engine of Watt. — Washborough and Pickard. — 
Crank. — Sun and Planet Wheel. — Other Inventions and Improvements 
by Watt. — Hornblower. — Watt's patent extended. — Governor.— Introduc- 
tion of steam into various mechanic arts. — Expiration of Watt's patent. — 
Cartwright and Sadler. — Murray, Maudslay,ancl Fulton. — Wooli. — Oliver 
Evans. — Trevithick and Vivian. — Rotary Engines. — Conclusion. 203 

CHAPTER IX. 

APPLICATIONS OF THE STEAM ENGINE. 

General view of the application of the Steam Engine. — Raising water. — 
Grinding corn. — Cotton Spinning. — Navigation. — Bossut's laws of the 
compact of fluids. — Principles of the action of Paddles. — Juan's laws of 
the action of fluids on solids moving in them. — Maximum speed of vessels. 



X CONTENTS. 

— Power required to propel paddles. — Relation between the power and the 
surface of the Paddles. — Laws of the motion of Steam-boats. — Theory of 
paddle wheels. — Comparison between theory and observation. — Sugges- 
tions for the improvement of Steam navigation. — Practical Rules. — Steam- 
boat engines. — History of Steam navigation. — Navigation of the Ocean 
by Steam. — Rules for boilers of Steam-boats. — Application cf Steam to 
Locomotion. — History of the Steam-Carriage. — Conclusion. 231 

Appendix. --__--•_- 285 






TREATISE, &d. 



CHAPTER I. 

MECHANICAL AND PHYSICAL PRINCIPLES THAT ARE APPLI- 
CABLE TO THE CONSTRUCTION OF THE STEAM ENGINE. 

Division of Material substances. — Forces which determine 
the state in which they exist. — Forms which all bodies are 
capable of assuming. — Difference in the mode of action of 
solids and fluids. — Forces and Motion. — Centres of Gra- 
vity, Inertia, Percussion, Oscillation, and Gyration. — Mo- 
tions found in natural agents, and in the parts of Ma- 
chines. — Mechanical properties of fluids. — Specific Gra- 
vities. — Pressure of the Atmosphere and Barometer. — Heat 
and its effects. — Thermometer. — Expansion of bodies by 
heat. — Specific Heat. — Latent Heat. — Evaporation. — Ra- 
diation of Heat. — Conducting Power of bodies. — Mode in 
which liquids carry off heat. — Cooling effect of gases. — 
Distribution of Heat among the particles of a solid. 

The material substances with which we are acquainted are 
either Solid or Fluid. 

Fluids are again subdivided into two classes, those which are 
incompressible, and those which are elastic : the former are 
called Liquids, the latter Aeriform Fluids. 

Elastic or aeriform fluids may either be capable of being rea- 
dily condensed into the liquid form, and are then called va- 
pours or steam ; or can only be reduced to that form with great 
difficulty, resisting in some cases all the means, whether me- 
chanical or physical, that have hitherto been applied for that 
purpose. The latter are styled gases, or permanently elastic 
bodies. 

1 



2 PRINCIPLES OF MECHANICS. 

The last-named class may, however, when in chemical com- 
bination, assume both the liquid and solid form, and there are 
but few that have not, in recent experiments, been converted 
into liquids, by pressures of greater or less intensity. Still, how- 
ever, although nearly the whole class are now known to be 
condensible, the distinction between vapours and gases may be 
here retained with propriety, inasmuch as there is a wide dif- 
ference in the manner in which they are applied in practical 
mechanics. 

2. Two great antagonist forces are concerned in determining 
in which of these mechanical states a body shall exist : these 
are, Attraction and Heat. To that species of attraction which 
takes place between the particles of one and the same body, 
whether it be simple or compound, in its chemical character, 
the name of Attraction of Aggregation has been given. When 
the intensity of the attractive forces, exerted mutually by the 
particles of a body, is greater than the action which heat exerts 
to separate them, the body will exist in the solid state ; when 
the action of attraction and heat exactly balance each other, the 
body is a liquid ; and when the repulsive force of heat predomi- 
nates, the body passes into the state of an elastic fluid. 

We know, however, of no perfect liquids ; in them all there 
remains a greater or less preponderance of the attraction of ag- 
gregation. This is manifested by the tendency they have, 
when minutely divided, to form small globular masses, or drops. 
And hence the motion of their particles among each other 
meets with a slight resistance, which is said to be due to the 
viscidity of the fluid. 

3. It may be considered as a general rule, that all bodies in 
nature are capable of existing, when properly influenced by 
heat, in either of the three mechanical forms. Thus, if we can- 
not, by mechanical or physical means, reduce the lighter gases 
to the solid form, still we find them assuming it in chemical 
combinations ; while nearly all, even of the most refractory 
solids, have been melted and rendered volatile under the intense 
heat of the Galvanic Deflagrator, or of the Compound Blowpipe. 



PRINCIPLES OF MECHANICS. 3 

4. The general principles of mechanics applyequally to solid 
and fluid bodies, but are modified in their action by the pecu- 
liar nature of each. Solid bodies, having their particles firmly 
connected together, act as if all the matter they contain were 
collected in a single point. When the body presses merely by its 
own weight, or when the motion is rectilineal, this point is the 
Centre of Gravity, or of Inertia ; if the body oscillates around 
a fixed point, it is the Centre of Oscillation or Percussion ; and 
when it revolves around an axis, it is the Centre of Gyration. 
The properties of these points, along with the general principles 
of motion, and the causes that produce it, are of constant value 
in considering the structure of the steam-engine and its parts. 
And although these are to be found in all books on the theory 
of mechanics, it has been considered proper to recapitulate 
them in a succinct manner, in order that they may be referred 
to in the course of the work. 

5. The cause which would tend to set a body in motion, 
whatever be its nature, is called a force. 

A body moves in the direction of the force impressed, and 
with a quantity of motion equal to the intensity of the force. 

A body set in motion by a force, and then abandoned to it- 
self, would continue to move uniformly forwards in a straight 
line, were not its direction and the intensity of its motion to be 
changed by the action of other forces. Thus, near the surface 
of the earth, the friction of other bodies, and the resistance of 
the air, act continually to retard and finally destroy the motion 
of bodies, while the attraction of the earth constantly tends 
to change the direction of the motion, and bring the body back 
to the surface. 

When a body is set in motion by a force which acts during 
the whole continuance of the motion, it will still describe a 
straight line, but the spaces described in equal times will gra- 
dually increase. If the force act with equal intensity upon the 
body, whether it be in rest or in motion, the motion is uniform- 
ly accelerated, and the force is said to be constant. All forces 
that act continually, whether constant or not, are called accele- 
rating forces. 



4 PRINCIPLES OF MECHANICS. 

When more than one force acts upon a body at the same in- 
stant of time, the direction and intensity of the motion will de- 
pend upon the joint action, and we may imagine it to be the ef- 
fect of a single force, whose direction and intensity correspond 
with the motion given to the body. Such a force, which, were 
the forces that really act withdrawn, would produce the same 
effect that they do, is called their Resultant ; the forces that it 
would thus identically replace, are called the Components. 

The resultant of two forces that act in the same straight line, 
and in the same direction, is equal to their sum ; if in the same 
straight line, and in opposite directions, it is equal io their dif- 
ference : generally, the resultant of any number of forces act- 
ing in the same straight line is equal to their algebraic sum, the 
difference of direction being denoted by the use of the positive 
and negative signs. 

The resultant of two forces whose directions are inclined to 
each other, and which meet in a point, is represented in magni- 
tude and direction by the diagonal of a parallelogram whose 
sides represent the direction and magnitude of the forces. The 
resultant of three forces is found, by taking, first, the resultant 
of two of them, and then combining this resultant with the 
third. The resultant of three forces thus found may be com- 
bined with a fourth, in order to find the resultant of four, and 
so on for any number of forces. 

When in a machine a force acts obliquely, no more of the 
force is effective than that which would be a component of the 
force in the line of direct action ; the other component is a loss 
of power, so far as the mechanical effect to be produced is con- 
cerned. It is, however, in general, worse than a mere loss of 
power ; for the whole of the force decomposed in this last direc- 
tion acts upon the machine itself, and generally to wear away 
or dislocate its parts. 

Motions are capable of being resolved or decomposed in the 
same manner as forces, and the investigation may in this way 
be extended to the case of forces that continue to act during the 
whole duration of the body's motion. 

A motion which grows out of the combination of two other 
oblique motions, is in the direction of the diagonal of the paral- 



PRINCIPLES OF MECHANICS. 5 

lelosfram whose two sides represent the magnitude and direction 
of the two forces, and the intensity of the motion is represented 
by the magnitude of the diagonal. When two oblique forces 
act, one of which abandons the body, and would thus produce 
an uniform motion, while the other continues to act during the 
whole duration, we conceive the motion to be divided into a 
great number of very small portions, during each of which the 
motion and direction remain constant : the body would then 
tend to go on in a straight line, at the end of each of the small 
intervals in which the small portions of the motion are per- 
formed, but is, during each of them, deflected into the diagonal 
of a parallelogram by the active force. In this way a polygon 
is formed, which, as the sides are inappreciably small, coincides 
with a curve. When, therefore, two motions oblique to each 
other are combined, one of which is uniform and the other ac- 
celerated, curvilinear motion is the consequence. 

If two accelerating forces act, in which the rate of accelera- 
tion is the same, the motion is rectilineal ; but if it be different, 
the motion is still curvilinear. 

When two parallel forces act upon a body, the resultant di- 
vides the line that joins the points to which the forces are ap- 
plied, into parts that are inversely proportioned to the intensity 
of the two forces, and the resultant is equal in magnitude to the 
sum of the forces. The resultant of three such forces is found 
by taking first the resultant of two of them, and combining it 
with the third ; this may again be combined with a fourth, and 
so on to any number. 

The resultant of any number of parallel forces continues of 
the same intensity, and passes through the same point, whatev- 
er be the direction of the forces ; hence it is called the Centre 
of Parallel Forces. When the body is moving forward in a 
straight line, under the action of forces other than gravity, it is 
called the Centre of Inertia ; when the body is acted upon by 
gravity, it is called the Centre of Gravity. 

6. By gravity, or the attraction of gravitation, is meant that 
force, by virtue of which all bodies fall towards the earth in 
lines perpendicular to its surface. Although these directions 



6 PRINCIPLES OP MECHANICS. 

are neither absolutely parallel, nor the forces, at different parts 
of the earth, or different distances from its surface, equal; still 
the convergence of the lines is so small, and the variation so 
slow, that there is no impropriety in considering every particle 
of the body as acted uprm by an equal and parallel force. 
The resultant of all these forces is the Weight of the body, and 
its place of action is the Centre of Gravity. 

When the centre of gravity is supported, the body is supported 
also; when the centre of gravity is not supported, the body will fall 
until the centre of gravity reaches the lowest possible point. 
The supporting force may be applied to the centre of gravity, 
or it may act at a point vertically above, or vertically beneath 
that centre. In the first case the position of the body is indif- 
ferent, and it will remain at rest, however placed around the 
point of support ; in the second case, the body, if once disturb- 
ed, will fall or move around the point of support, until this be 
vertically above the centre of gravity ; in the third case, if the 
body be disturbed, it will oscillate until it return to rest in the 
position it originally held. 

The centre of gravity of a straight line bisects it. 

The centre of gravity of a cylinder, or of a spindle of symmetri- 
cal form, bisects the axis. 

The centre of gravity of a circle corresponds with its centre, 
as does that of a sphere. 

The centre of gravity of a triangle is in the line which joins 
its vertex to the point that bisects its base, and at the distance 
of two-thirds of this line from the vertex. 

When the centre of gravity of a triangle is known, that of a 
quadrilateral figure may be determined by dividing it into two 
triangles, and finding their respective centres of gravity, whence 
the common centre may be determined, as it will divide the 
line that joins the two, into parts inversely proportioned to the 
size of the two triangles. The centre of gravity of a pentagon 
is found by dividing it into three triangles, and thus for any 
polygon whatsoever. 

The centre of gravity of a triangular pyramid is in the line 
which joins the vertex of the pyramid to the centre of gravity 



PRINCIPLES OF MECHANICS. 7 

of the base, and at a distance of three-fourths of this line from 
the vertex. 

When the centre of gravity of a pyramid is determined, we 
have the means of finding that of any solid body bounded by 
plane surfaces, for it may be divided into triangular pyramids. 

The centre of gravity of a solid cone is in the line which joins 
its vertex to the centre of its base, and at the distance of three- 
fourths of that line from the vertex. But the centre of gravity 
of the surface of a cone is at the distance of two-thirds of that 
line from the vertex. 

The centres of gravity of an ellipsis and an ellipsoid of revo- 
lution correspond with their respective geometric centres. 

When a body is attached to a fixed point and oscillates, the 
action is no longer such as would take place if the whole of the 
matter were collected in the centre of gravity ; but the point, in 
which, if all the matter were collected, the action would be the 
same as actually takes place, is farther from the place of suspen- 
sion ; this point is called the centre of oscillation. 

The centre of oscillation of a straight line is distant two- 
thirds of its length from the point of suspension. 

The centre of oscillation of a triangle is at the distance of 
three-fourths of its height from the vertex. 

The centre of oscillation of a cone, right angled at the ver- 
tex, is in the middle of the base. 

The centre of percussion is that point in a striking body, at 
which the whole of the motion would be communicated to the 
body struck. 

When the striking body moves round a fixed point, the cen- 
tre of oscillation and centre of percussion are identical. 

A body suspended from a fixed point, and oscillating under 
the action of gravity, is called a Pendulum. 

The centre of Gyration is that point in a revolving body, in 
which, if all the matter were collected, the quantity of rotary 
motion would remain the same as before. 

The centre of gyration of a straight line, moving around an 
axis passing through one of its extremities, is at a distance from 
that axis, which bears to the length of the line the ratio of one 
to the square root of three, 1 : V3. 



8 PRINCIPLES OF MECHANICS. 

The distance of the centre of gyration of a circle or circular 
sector from its centre of rotation and curvature, is to the radius 
of the circle, as one to the square root of two, 1 : V2. 

The motions which we find in the parts of machines, and in 
the great natural agents that are employed to propel them, are 
either rectilineal or rotary. Rectilineal motion may be either 
continuous or reciprocating, and rotary motions may in like 
manner either go on continually, or the moving points may os- 
cillate within certain limits, and thus reciprocate. 

Among these four species of motion, taken by pairs, there are 
ten possible combinations, and these might therefore occur in 
the changes which a machine makes upon the original motion 
of the moving power, or which one part of a machine causes 
in the motion of another ; no more than eight of these combina- 
tions, however, are to be met with in practice. 

a. A continuous rectilineal motion is sometimes converted 
into another continuous and rectilineal motion, in an opposite 
direction. 

6. A continuous rectilineal motion is sometimes changed into 
a continuous rotary motion, or, 

c. Into a reciprocating rotary motion. 

d. A continuous circular motion is sometimes changed into 
an alternating rectilineal motion. 

e. A continuous circular motion is sometimes changed into 
another continuous circular motion, in an opposite direction, 
or, 

f. Into a reciprocating circular motion. 

g. A reciprocating rectilineal motion is sometimes changed 
into a reciprocating circular motion. 

h. A reciprocating circular motion is sometimes changed 
into another reciprocating motion in an opposite direction. 

8. The particles of fluid bodies, having no, or at most an in- 
sensible, attraction of aggregation, act independently of each 
other. Hence, we cannot refer the motion of a fluid mass to 
either of the Centres of which we have spoken, but each par- 
ticle moves freely under the forces that are impressed, whether 



PRINCIPLES OF MECHANICS. 9 

they act immediately upon it, or through the intervention of 
the adjacent particles. 

Fluids thus transmit any force applied to one of their surfaces 
equally in all directions ; and if a fluid be inclosed in a vessel, 
and a force act upon any portion of its surface, as by means of 
a piston perforating one of the sides of the vessel that contains 
it, the pressure upon every remaining portion of the vessel will 
be equal, upon an equal surface, to that acting upon the piston : 
thus, if the piston be a square inch, and be acted upon by a 
force equivalent to a pound, every square inch of the surface of 
the vessel will also have to sustain a pressure equivalent to a 
pound. 

When a fluid is kept in equilibrio in an open vessel by ex- 
traneous forces, these forces must act perpendicularly to the un- 
covered surface of the fluid, and if the fluid be acted upon by 
gravity, its surface must therefore be horizontal, or perpendicu- 
lar to the direction of gravity. In a small vessel, the surface is 
a horizontal plane, inasmuch as the forces may be considered 
as acting in parallel lines ; but in large masses of gravitating 
fluids, as the ocean or great lakes, the surface becomes a curve 
parallel to the general figure of the earth. 

Any line drawn upon such a surface, or parallel thereto, is 
called a level line, or more simply, a Level. 

When a gravitating fluid is placed in a bent tube, or in ves- 
sels communicating at bottom, it rises in the two branches of 
the tube, or in the several vessels to the same level. And if a 
pipe be inserted in a close vessel, the pressure on the sides of it 
will be proportioned to their surface, and the height of the fluid 
in the pipe. If the fluid in the pipe be acted upon by some ex- 
trinsic force, the action will be transmitted to the sides of the 
vessel, and the whole pressure upon them will be as much 
greater than the pressure upon the fluid in the tube, as the sur- 
face of the vessel is greater than the area of the tube. This 
principle has been applied to the construction of an instrument, 
in which a small force, acting through the intervention of a li- 
quid, is made capable of exerting an intense pressure. It is 
called the water-press pump, or, after the name of the inventor 
Bramah's press. The pressure of a gravitating fluid upon a 

2 



10 PRINCIPLES OP MECHANICS. 

horizontal base, is not proportioned, as in solid bodies, to the 
mass or weight of the fluid, but to the surface, and the height 
of the level surface of the fluid above the base. The measure 
of such pressure is the weight of a parallelopepid of the fluid, 
whose base is equal in area to the base of the vessel, and whose 
altitude is equal to the depth of the fluid. It is therefore the 
same, whatever be the capacity or shape of the vessel, provid- 
ed the area ot the bottom and the depth of the fluid remain- 
constant. 

Upon surfaces that are not horizontal, the measure of the 
pressure of a gravitating fluid is the weight of a parallelopepid 
of the fluid, whose base is equal in area to the surface pressed, 
and whose altitude is equal to the depth of the centre of gravi- 
ty of that surface beneath the level of the fluid. 

Although the pressure upon a given surface depends upon 
the position of its centre of gravity, yet this is not the point to 
which the resultant of the hydrostatic pressure is applied. 
This last point is called the Centre of Pressure, and it coincides 
with the point which would be the centre of oscillation of the 
surface. Hence, in the calculations of the strength of the sides 
of vessels, or of walls to contain masses of fluids, the resultant 
of the resistances they oppose must pass through this point, 
and be at least equal to the hydrostatic pressure of the fluid. 

When a body is placed in a fluid whose weight is less than 
that of an equal bulk of the fluid, it rises and floats at the sur- 
face, and as much of it is immersed as displaces a mass of the 
fluid whose weight is equal to its own. 

In general, if any solid body be placed in a fluid, it will, if 
lighter, rise to the surface ; if heavier, sink to the bottom ; and 
the force with which it will rise or sink, will be equal to the 
difference between its own weight and the weight of an equal 
bulk of the fluid. Hence, a body immersed in a fluid loses as 
much of its weight as is equal to the weight of a mass of fluid 
of equal bulk. 

Were the particles of fluids to move independently of each 
other, they would issue from an orifice in the bottom or side of 
a vessel that contains them, with the velocity a falling body 
would acquire in descending from the surface of the fluid to the 



PRINCIPLES OF MECHANICS. 11 

level of the orifice, and the section of the stream would be equal 
to the area of the orifice, and of the same size everywhere. 
But in consequence of the mutual action of the particles, the 
stream, in passing through an orifice cut in a thin plate, does 
not continue of the same area with the orifice ; it is at first con- 
tracted, and if the orifice be circular, the place of greatest con- 
traction is at a distance from the vessel equal to the radius of 
its orifiee ; the shape of the jet is a truncated cone, whose great- 
er base is equal to the area of the orifice, and whose least bears 
to it the proportion of 5 : 8. An opening in a thick-sided ves- 
sel discharges more, and pipes of different forms give greater 
or less increases to the above ratio. The quantity of fluid is 
measured by multiplying the velocity by the area of the less 
base of the truncated cone, which is called the Vena Contractu, 

9. The comparative weight of equal bulks of different bodies 
Is called their Density. We usually compare these by means 
of a conventional standard, whose density forms the unit in 
which the densities of the rest are estimated. Densities thus 
estimated are called the Specific Gravities of the bodies, and the 
body employed as the standard in most cases, is Water. 

In estimating specific gravities, it is not merely necessary that 
the water be pure, but, as both the bodies are capable of assum- 
ing different densities at different temperatures, it is necessary 
to define the temperature at which the experiments shall be 
made. The best temperature for this purpose is, for reasons 
we shall hereafter state, from 38° to 40° of Fahrenheit's ther- 
mometer. To determine specific gravities, we make use of the 
principle that a body loses in water as much weight as is equi- 
valent to the weight of an equal bulk of water. If, then, a body 
be weighed in air, and afterwards in water, the difference is the 
weight of an equal bulk of water ; and as water is the 
unit, we have only to divide the weight in air by the loss of 
weight, and the quotient is the specific gravity. 

The instrument by which specific gravities are thus deter- 
mined, is called a hydrostatic balance. It differs from a com- 
mon balance only in having a convenient apparatus added 
by which the weight in water can be determined. 



12 



PRINCIPLES OP MECHANICS. 



It sometimes becomes necessary to determine the specific gra- 
vity of bodies lighter than water. In this case the body, after 
being weighed in air, is attached to a body sufficiently heavy 
to cause it to sink, and whose weight in air, and weight in wa- 
ter are known. The dividend is, as before, the weight of the 
light body in air, the divisor is the difference between the loss 
of weight of the heavy body, and the loss of weight of the two 
united. 

The Specific Gravities that are of most frequent use in the 
construction of steam engines, are as follows, viz. 

Table of Specific Gravities. 






" 


Water at its maximum density, 


1.000 


Mercury, ------ 


13.568 
11.352 




Copper, Cast, - 


S.78S 


Rolled, ... - 


8.878 


Brass, Cast, - - - - 


8.396 


Rolled, - 


8.544 


Iron, Cast, - 


7.207 


Wrought, 


7.788 


Steel, Hard, ------ 


7.S16 


Soft, 


7.833 


Tin, ------ 


7.291 




7.190 


Sea Water, - 


1.026 


Dry Oak, 


0.932 


Yellow Pine, - - - - - 


0.657 


White Pine, ----- 


0.569 








10. When two fluids of different densities press against each 
other in opposite branches of a bent tube, they will come to 
rest in their respective branches, at heights above the common 
level inversely proportioned to their respective densities. 

Upon this last stated principle, we may determine the pres- 
sure of the mass of elastic fluid which surrounds our Earth, 
and which is called the Atmosphere. If a piston be fitted air 
tight, in a glass tube about three feet in length, and the lower 
end immersed in a vessel of mercury, the tube being held in a 



PRINCIPLES OP MECHANICS. 13 

vertical position, and if the piston be drawn upwards, the mer- 
cury will follow the piston as it ascends in the tube, being 
forced up by the pressure of the atmosphere. When, however, 
the piston reaches a height of about thirty inches, the mercury 
will cease to follow, and an empty space will be left between 
its surface and the lower side of the piston. 

In like manner, if a tube, closed at one end, be filled with 
mercury, and being closed by the finger, inverted, and the open 
end plunged in a basin of mercury, the mercury will remain 
suspended in the tube if its length be less than thirty inches ; 
but if it be longer, and the tube be held vertically, the mercury 
will descend, flowing into the basin until its surface stand at a 
level of about thirty inches above the surface of the mercury in 
the basin. 

This height of thirty inches is not constant, but varies in the 
same place, in consequence of changes which are constantly oc- 
curring in the pressure of the atmosphere ; it also varies in dif- 
ferent places, in consequence of their being at different eleva- 
tions above the level of the sea, and bearing, in consequence, 
columns of air of varying depths ; but at the level of the sea, 
the mean pressure is such as will support thirty inches of the 
mercury. 

Now, according to the principle we have laid down, the pres- 
sure of this column of mercury upon a base of a square inch, 
will be equal to the weight of thirty cubic inches of mercury. 
This is almost exactly fifteen pounds, at which it is usual to 
estimate the pressure of the atmosphere upon every square inch 
of the surface of bodies subjected to it. This pressure, being 
that of a fluid, is equal in all directions ; and hence is impercep- 
tible to us, unless when it is taken off upon one part of a body, 
when that exerted on the opposite side becomes sensible. So 
far from tending to crush bodies placed in it, the atmosphere 
rather acts to support them, by bearing as much of their weight 
as is equal to the weight of an equal bulk of atmospheric air. 

11. If the sealed tube be not entirely filled with mercury, a 
portion of air remains in it ; when the finger is pressed on the 
open end and the tube inverted, the air rises to the closed end 



14 PRINCIPLES OF MECHANICS. 

of the tube ; and when the apparatus is plunged in a basin of 
mercury, and the finger removed, the air within, being no long- 
er compressed by the whole force of the atmosphere, will in- 
crease in bulk, and occupy a greater space than it originally 
filled, forcing out a part of the mercury. 

It is a law which holds good in all elastic fluids, that they oc- 
cupy spaces which are inversely as the pressures to which they 
are subjected, and their densities are in consequence in the di- 
rect ratio of the pressures. Hence the difference between the 
height of the mercury in the tube that contains air, and that to 
which it rises in one void of air, will be the measure of the den- 
sity of the air thus contained, or of the pressure of any other 
elastic fluid separated by a column of mercury from the open 
atmosphere. 

The experiment, with a tube containing mercury, and in- 
verted in a basin of the same liquid, by which we measure the 
pressure of the atmosphere, was planned by Torricelli, and goes 
by his name. The apparatus, when attached to a support, and 
furnished with a scale on which the height of mercury in the 
tube can be measured, is called a Barometer. Of this there are 
several forms, and it is applicable to many important uses ; of 
these, however, it is not our province to treat. 

The same force which is capable of raising a column of mer- 
cury thirty inches in height, is capable of raising a column of 
water as much longer as the specific gravity of mercury is 
greater than that of water. This height is about thirty-four 
feet. Hence, if by any means a vacuum be made in a tube 
whose height is not greater than thirty-four feet, and its end 
be plunged in a mass of water, the fluid will rise and fill it. If 
the vacuum be imperfect, the water will still rise, but to a less 
height. Such is the principle upon which the common pump 
acts, where a piston, furnished with a valve opening upwards, 
and moving with reciprocating motion in a tube, also furnished 
with a valve opening upwards, exhausts a portion of air at each 
stroke, whose place is supplied by an equal quantity of water, 
until the water rises through the valve of the piston, and is lift- 
ed by it to the spout of the pump. Such also is the cause 
which supports a fluid in the branches of a syphon tube, 



PRINCIPLES OF MECHANICS. 15 

whence it will flow with a force depending upon the difference 
in level, of the surface of the fluid in the vessel to which it is 
applied, and the open end of the syphon. 

The Torricellian apparatus may not only be made the mea- 
sure of the pressure of the atmosphere, and of the elaslicity of 
gaseous matter contained in its tube, but may be applied to 
measure the pressure of any fluid immiscible with mercury, 
whether elastic or not. Neither is it necessary that its open 
end be immersed in a basin of mercury ; but if it be turned up 
like an inverted syphon, the fluid whose pressure is to be measur- 
ed, will act upon its open end, and the measure of the pressure 
will be a column of mercury whose altitude is the difference of 
the level of that fluid in the two branches of the tube. 

Jf both ends of the bent tube be open, but, while the one 
communicates with the atmosphere, the other is acted upon by 
a fluid contained in a close vessel, the difference of the two 
levels of the mercury will now be the measure of the excess or 
defect of the pressure of the confined fluid, above or below the 
pressure of the atmosphere. 

11. The great natural agent which, as we have said, acts in 
opposition to the attraction of aggregation, is Heat. Of its ac- 
tual nature we know nothing, and it would be worse than use- 
less to enter here into a consideration of the different hypothe- 
ses that have been framed in respect to it. It is, however, ca- 
pable of acting upon our senses, producing the sensation of 
warmth, and of exercising influences of various natures upon 
all bodies. By means of these actions which determine 
its properties, it may be studied, and the laws of its action as- 
certained. 

The first effect of heat of which we shall treat, is that of ex- 
panding the bodies submitted to its action. It is a general law, 
that all bodies increase in bulk when heated, and contract 
when cooled. But the manner and rate of their expansion and 
contraction differ, both with the mechanical and individual na- 
ture of the substances. 

Of solids, each different species expands at a different rate ; 



16 PHYSICAL PRINCIPLES. 

but in all bodies of the same material the expansion is equal 
for equal increments of temperature. 

In liquids, not only does each different liquid expand at a 
different rate, but the same liquid expands unequally for equal 
increments of heat at different temperatures. The expansion 
is least rapid when the temperature is not far from that at 
which the liquid congeals, and is most rapid as it approaches 
that at which the liquid boils. 

In elastic fluids, whether gases or vapours, not only is the ex- 
pansion of each uniform for equal changes of temperature, but 
the rate of expansion is identical in them all. 

12. We apply this property of heat to the construction of in- 
struments for measuring its intensity ; such instruments are 
called Thermometers. They are now usually composed of a 
small tube, on the end of which a bulb is blown, and in which 
a portion of mercury is placed. The mercury is heated until 
it either fill the tube by its expansion, or, if the scale be in- 
tended to be long, with its vapour ; the end is then closed by 
heat. When the mercury cools, it shrinks in the tube, and 
leaves the upper part free ; and it will occupy a different space 
according to the temperature to which it is heated. To make 
such instruments capable of comparison with each other, it is 
necessary to adopt fixed points that may be easily obtained in 
all places. Of these, there must be at least two ; and those 
which are now universally used, are what are usually called 
the Boiling and Freezing Points of water. 

It is, as we shall see hereafter, a well-established fact, that the 
water which runs from melting ice is of the same temperature 
under all possible circumstances ; and that the heat of boiling 
water under equal atmospheric pressure is also constant. In 
the latter case, therefore, it is necessary to define the pressure 
at which the experiment shall be made, and this has been esta- 
blished by usage at the mean pressure of the atmosphere at the 
level of the sea, or when the Barometer stands at 30 inches. 

The scale which is usually employed upon thermometers in 
this country and in England, is that of Fahrenheit. This has 
the number 32 opposite to that point in the stem of the instru- 



PHYSICAL PRINCIPLES. 17 

ment where the mercury stands in melting ice ; this is called 
the freezing point. Between this and the point at which the 
mercury stands in water boiling, when the barometer has a 
height of thirty inches, the space on the stem of the instrument 
is divided into 180 equal parts. Opposite to the temperature 
of boiling water therefore, the number 212°, equal to 180°-f-32°, 
is placed. The mark 0° is thirty-two divisions or degrees be- 
low the freezing point ; and as mercury is capable of bearing, 
without congealing, even lower temperatures, and as they have 
actually been observed and may become the object of experi- 
ment, the scale is extended below this point as far as 40 equal 
divisions ; these are also called degrees ; but to distinguish them 
from those above 0°, and to enable such temperatures to be 
made use of in calculation, the numbers are arranged in in- 
verted order, and distinguished by the negative sign. 

To measure any temperatures that are not greater than that at 
which mercury boils, the scale is carried upwards, also by equal 
degrees, to about 600°. Mercury boils at 575°, and freezes at 
— 40° ; and thus the whole scale of Fahrenheit includes 615 
equal divisions or degrees. 

Mercury, like other fluids, is subject to the law of a diminish- 
ed expansion near the point of its own congelation, and one 
increased near the temperature of its boiling ; hence the equal 
divisions on the scale do not correspond exactly with equal in- 
crements of temperature. But, as the rate of expansion is very 
nearly uniform at all mean temperatures, at which by far the 
greater portion of philosophical inquiries are made, no practical 
error of any importance can arise from considering the de- 
grees of the thermometric scale as corresponding to equal chang- 
es of heat. 

13. Furnished with such a measure of heat, experiments 
may be made upon the expansion of the several classes of bo- 
dies. The results of such of these as are most important in refer- 
ence to our subject are given in the following table, viz. 



18 



PHYSICAL PRINCIPLES. 



Lineal dilatationof some of the metals for each degree of Fah- 
renheit s thermometer ; expressed in decimals of their length 
at the temperature of Melting Ice. 





- 


Copper, ----- 


0.0000096 


Brass, - 


0.0000104 


Wrought Iron, - 


0.0000068 


Cast Iron, - 


0.0000061 


Soft Steel, 


0.0000059 


Tempered Steel, - 


0.0000069 


Lead, - 


0.0000158 


Tin, 


0.0000121 



The cubical expansion of these bodies can be deduced from 
the above table, for it is a fact that is confirmed both by theory 
and experiment, that the fraction, which represents the expan- 
sion of any body in bulk, is just three times as great as that 
which represents its lineal expansion ; the solid contents being 
taken as unity in the first case, and the length in the second. 
The whole dilatation of Water between its freezing 
and boiling points, is ----- aV 

Of Alcohol, between the boiling and freezing points 
of water, ------- -£ 

Of Mercury, - - - - - - - sV 

Within these limits the expansion of mercury is tolerably 
uniform ; indeed, if contained in a glass tube, the joint efFect of 
the expansibilities of the two bodies is to produce absolute uni- 
formity, but water is not only liable to unequal rates of expan- 
sion at varying temperatures, but is also subject to a remarka- 
ble anomaly. When water is taken as it flows from melting 
ice, so far from expanding by the first application of heat, it 
contracts. This contraction continues until it reaches the tem- 
perature of 38° ; from this point until it be heated to 40° its 
bulk undergoes no perceptible change ; heated beyond 40°, it 
begins to expand, and continues to do so in an increasing ratio 
until it begins to boil. Hence water is at its maximum of densi- 
ty at a temperature of from 38° to 40°, and this being a physi- 



PHYSICAL PRINCIPLES. 



19 



cal state that can be defined independent of the thermometer, 
it is then best suited to be used as the unit in determining spe- 
cific gravities. 

The densities of water at various temperatures are as follows, 
viz. 



■ 









32° 


.99989 


79o 


.99682 


34o 


.99995 


1000 


.99299 


39o 


1.00000 


122o 


.99753 


440 


.99995 


142^ 


.98182 


490 


.99978 


162o 


.97552 


5-1° 


.99952 


182o 


.96891 


59° 


.99916 


202o 


.96198 


69° 


.99814 


212° 


.95860 


1 






.. , 



When water congeals, it suddenly expands, increasing in 
bulk one-ninth part of its former dimensions. By this sudden 
dilatation it becomes capable of producing the most powerful 
mechanical effects. Other substances also expand suddenly on 
passing from a fluid to a solid state ; among these is cast iron, 
and this expansion is among the most important of the practi- 
cal difficulties that attend the making of the parts of steam en- 
gines. 

We have stated that all elastic fluids not only expand uni- 
formly, but that the rate of expansion is the same in all. By 
the experiments of Dal ton and of Guy Lussac, this dilatation is 
found to be 0.375 of the bulk between the temperatures of 
freezing and boiling water, or 0.00208 for every degree of Fah- 
renheit's thermometer. 



14. When bodies are exposed to the action of heat, even 
when it is not sufficiently intense to produce any change in 
their mechanical state, they are found to be unequally affected 
in temperature by equal intensities of heat. Thus, for instance, 
the heat necessary to raise the temperature of a pound of water 
3 A } will be sufficient to heat an equal weight of mercury 
100°, The heat thus absorbed by different bodies, in raising 



20 



PHYSICAL PRINCIPLES. 



equal weights an equal number of degrees is called their Spe- 
cific heat. We know nothing of its absolute quantity, and are 
therefore compelled to express merely the ratio between the 
specific heats of the different substances, and this is usually done 
by taking the specific heat of water as unity. 

Specific Heat of different bodies between the temperatures of 
Boiling and Freezing Water, according to Messrs. Petit 
and Dulong. 





= -I 


Water, - 


1.0000 


Mercury, - 

Platina, - - - - 


0.0330 
0.0335 


Copper, ------ 

Iron, ------- 


0.0940 
0.1098 


Atmospheric Air, - - - - 


0.2669 


Hydrogen, ------ 

Oxygen, 

Steam, 


3.2936 

0.2361 
0.8470 



All bodies, when compelled to change their volume, have 
their capacities for specific heat affected. When they are con- 
densed their capacity is diminished ; when they expand their 
capacity is increased. Hence, in the former case their temper- 
ature is elevated, in the latter it is lowered. In solid bodies 
that are not elastic, percussion and pressure heat them, and in 
some cases until they are red hot. The heat evolved at first is 
the greatest, and they finally, when the density becomes the 
greatest that the pressure can produce, cease to be further heat- 
ed. In liquids the small increase of temperature that is caused 
by pressure, is exactly compensated when the pressure is re- 
moved. Gases and vapours are also affected in a similar man- 
ner ; when they are condensed their temperature is raised, when 
they expand it is lowered. Steam is also subject to the same law, 
and thus when allowed to escape from a vessel in which it is 
generated under pressure, it rapidly assumes, in expanding, the 
temperature that belongs to steam generated under the lessened 
pressure to which it is now exposed. 



PHYSICAL PRINCIPLES. 21 

15. When ice at a temperature below 32° is exposed to the 
action of heat, its temperature is readily raised to that degree ; 
here the elevation of temperature suddenly ceases, the ice be- 
gins to melt, and no farther increase of temperature can be at- 
tained until the whole of the ice be melted. It is hence infer- 
red that a portion of the heat applied, and which becomes in- 
sensible, is necessary to the constitution of the liquid, and re- 
sides in it in a state we call Latent. 

In the same manner, the water proceeding from melting ice 
begins to shew an increasing temperature as soon as the whole 
of the ice is melted ; the temperature continues to increase un- 
til it be raised to 212°, at this point the liquid begins to boil, 
or throw off steam rapidly, but the temperature of the water 
cannot be increased any longer. The steam that rises from the 
water has a similar temperature with the boiling liquid, and we 
infer from these two facts, that heat also passes into the latent 
state when it converts water into steam. When the steam re- 
turns to the state of water, and water passes into the state of ice, 
the heat that became latent in the previous change is again 
given out, and becomes sensible. To distinguish between 
sensible heat and that which is specific or latent, we employ, to 
designate the former, the term Temperature, — a word we have 
hitherto been compelled to make use of without explaining it. 

The quantity of sensible heat which becomes latent on the 
liquefaction of ice is about 135° of Fahrenheit. 

The quantity of sensible heat which becomes latent when 
water passes to the state of steam under the mean pressure of 
the atmosphere, is about 990°. 

But water, as we shall see, is capable of forming vapour at 
all temperatures. It is found, that in every case the sum of the 
sensible and latent heat is a constant quantity, and is equal 
to about 1100°. 

All other cases of liquefaction and evaporation are attended 
with similar phenomena of latent heat ; and it is a general law, 
that whenever a body changes its mechanical state, its relations 
to temperature are also changed. 

16. When the surface of a liquid is exposed, either at ordi- 



22 PHYSICAL PRINCIPLES. 

nary temperatures, or submitted to the action of heat, the liquid 
is gradually dissipated. The same dissipation takes place in a 
greater degree when the pressure of the atmosphere is lessened 
or removed altogether. At some particular temperature, under 
the mean pressure of the atmosphere, liquids throw off vapours 
with great rapidity, and the process, which is attended with a 
violent agitation, is called ebullition. If the pressure be lessen- 
ed, ebullition takes place at a lower temperature, until in the 
vacuum of an air-pump, water will boil below the heat of the 
blood. When the liquid is heated in a close vessel, it may be 
raised, under an increased pressure, to a temperature far above 
that at which it boils in the open air. The steam generated in 
all these cases has the same temperature as the liquid whence 
it flows, and contains, besides, heat in a latent state, according 
to the law we have just stated. The expansive force of steam, 
at various temperatures, is very different. At 212° it just ex- 
ceeds the pressure of the atmosphere, and hence becomes ca- 
pable of escaping from an open vessel in quantities just suffi- 
cient to carry off, in a latent state, all the heat that is commu- 
nicated to the liquid, which, when it has once reached this tem- 
perature, does not grow warmer until the whole be evaporated. 
The general law of the tension or expansive force of aqueous 
vapour is, that while the heat increases in arithmetic progres- 
sion, the expansive energy increases in a geometric ratio. It is 
usually stated that its pressure doubles for every 40° of Fah- 
renheit. A more exact measure of the tension of steam is de- 
duced from the experiments of Dulong and Arago. Their re- 
sults are comprized in the following table. 



PHYSICAL PRINCIPLES. 

Table of the Elastic Force of Steam. 



23 



Temperature. 


Pressure in 
Atmosphere. 


Pressure per 
Sq. in. in lbs. 


Temperature. 


Pressure in 
Atmosphere. 


Pressure per 
Sq. in. in lbs. 




212° 


1 


15 


380.6° 


13 


195 




242 


n 


22| 


387 


14 


210 




250.6 


2 


30 


392.6 


15 


225 




264 


n 


m 


398.5 


16 


240 




277.2 


3 


45 


403.8 


17 


255 




285.2 


H 


52^ 


409 


18 


270 




293.8 


4 


60 


413.8 


19 


285 




301 


H 


67,i 


418.5 


20 


300 




308 


5 


75 


423 


21 


315 




314.4 


5£ 


82^ 


427.3 


22 


330 




320.4 


6 


90 


431.4 


23 


345 




326.3 


H 


97i 


435.6 


24 


360 




331.2 


7 


105 


438.7 


25 


375 




341.8 


8 


120 


457.2 


30 


450 




350.8 


9 


135 


472.8 


35 


525 




359 
366.8 


10 


150 


480.6 


40 


600 




11 


165 


499.1 


45 


675 




1 374 


12 


180 


510.6 


50 


750 





To find the force with which steam tends to burst the ves- 
sels in which it is generated or confined, 151bs. must be deducted 
from the numbers in the third column of the above table, inas- 
much as the pressure of the atmosphere acts in opposition to 
the elastic force of the steam. 

The density and volume of steam at different temperatures 
may be ascertained by means of the following table, in which 
the density and volume of steam, estimated in relation to water, 
taken as the unit, are given for elastic forces estimated in at- 
mospheres. 



21 



PHYSICAL PRINCIPLES. 



Table of the Density of Steam under Different Pressures. 



r — 




i 


Pressure in 
Atmospheres. 


Density. 


Volume. 


1 


0.00059 


1696 


2 


0.00110 


909 


3 


0.00160 


625 


4 


0.00210 


476 


5 


0.00258 


387 


6 


0.00306 


326 


8 


0.00399 


250 


10 


0.00492 


203 


12 


0.00581 


172 


14 


0.00670 


149 


16 


0.00760 


131 


18 


0.00849 


117 


20 

L _ 


0.00937 


106 



The foregoing tables are only applicable to the case where 
water is heated in its liquid form, and when a portion of it re- 
mains to furnish matter to increase the density of the steam as 
its temperature rises. But when steam is heated out of contact 
with water, its tension increases only at the same rate as that 
of a gas. The latter case, however, rarely occurs in the use of 
steam for mechanical purposes. 

When water holds saline substances in solution, the tempera- 
ture at which it boils is raised in consequence of the attraction 
which exists between the liquid and the salt. It happens in 
some cases that the water of the ocean must be used in the 
generation of steam ; the change which the salts it contains pro- 
duces in its boiling temperature ought therefore to be known. 
Sea water is not of equal strength in all places, but no sensible 
error can arise from taking the experiments of Dr. Murray as 
the standard. He makes the density of sea water 1,029, and 
states, that in 10,000 parts there are contained : 
Muriate of Soda, - - 220 

Sulphate of Soda, 33 

Muriate of Magnesia, 42 

Muriate of Lime, 8 



303 



PHYSICAL PRINCIPLES. 25 

or about -^ pt- of the water. At this density the boiling 
point is 213.2. 

When, however, a boiler is fed with sea water, the strength of 
the solution will continually increase, as no part of the salts 
will be carried off with the vapour, until saturation takes place. 
The boiling point will therefore be continually rising, as repre- 
sented below. 



Salt in 


10,000 pts. i 


)f water. 




Boiling point. 


Saturated, 


3637 


- 


- 


226° 




3334 


- 


- 


224,9 




3030 


- 


- 


223,7 




2728 


- 


- 


222,5 




2425 


- 


- 


221,4 




2122 


- 


- 


220,2 




1813 


- 


- 


219,0 




1515 


- 


- 


217,9 




1212 


- 


- 


216,7 


: 


909 


- 


- 


215,5 




606 


- 


. 


214,4 




303 


- 


_ 


213,2 



At these several degrees of solution, the vapour at the cor- 
responding temperature has the same tension with that of pure 
water at 212°, or is equivalent to a single atmosphere. Start- 
ing from these several boiling points, the tension of the vapour 
will be increased exactly in the same ratio as that of pure wa- 
ter. Thus it may be stated approximately that the tension dou- 
bles for every elevation of 40° in the temperature j or, more ex- 
actly, the tension of the vapour of the solution at any given 
temperature may be obtained by deducting from that tempera- 
ture the excess of the boiling point of the solution over 212°, 
and seeking the tension corresponding to the difference in the 
table on page 23. 

When water, or any other liquid, is subjected to the action of 
heat in a close vessel, it rapidly attains its boiling temperature ; 
the vapour thus thrown off adds to the pressure of the enclosed 
atmosphere, and retards the boiling. The temperature of the 
liquid will then rise beyond the temperature at which it boils 
in the open air, until it reach a limit which varies in each 

4 



26 PHYSICAL PRINCIPLES. 

different liquid. At this last temperature, the whole mass of 
fluid is at once transformed into vapours of a great density, 
which fill the whole of the vase. 

As the elastic force of the vapour, which is formed in a close 
vessel, increases with great rapidity with the elevation of tem- 
perature, it follows that the vessels in which liquids are thus 
enclosed to the action of heat, ought to be very strong, and ca- 
pable of resisting a powerful pressure. But, whatever be their 
strength, if there were no limit to the temperature of the liquid, 
the time must arrive when the expansive force of the vapour 
would exceed the cohesion of the vessel, and burst it into pieces 
with great violence. 

The means that may be resorted to, to limit the temperature 
of a liquid enclosed in a vessel, will be considered when the 
structure of the boilers is treated of. 

We have just stated, that when a liquid was heated in a close 
vessel, the atmosphere of vapour formed within it would re- 
tard the ebullition until a certain period, when the whole li- 
quid mass would assume the form of vapour. This remarka- 
ble fact was discovered by Cagniard de la Tour. His experi- 
ments give the following results. (1.) Ether is wholly con- 
verted into vapour in a close vessel, at the temperature of 302°, 
in a space less than twice its original bulk, and exerts an ex- 
pansive force equal to 70 atmospheres. (2.) Sulphuret of Car- 
bon is wholly converted into vapour at a temperature of 420°, 
and has an expansive force of 37 atmospheres. (3.) Alcohol 
and water have exhibited similar phenomena ; the exact cir- 
cumstances under which they change their state have not been . 
observed, but it has been found that alcohol, becoming vapour 
of three times its liquid bulk, exerted a force of 119 atmos- 
pheres; and that water, at a temperature about that at which 
zinc melts, or 680°, expands at once into vapour of about four 
times its original bulk, exerting so great a force, that the experi- 
ment has been butseldom successful, in consequence ofthe break- 
ing of the vessels in which it has been attempted to perform it. 

17. Heat is conveyed in various manners : It may proceed 
directly from a heated body to those which surround it ; it may 



PHYSICAL PRINCIPLES. 27 

be conveyed through intervening bodies, or from one part of a 
body to another ; and in fluids it is distributed throughout the 
whole mass, by the motion itself generates among their particles. 

When a body, at any temperature whatsoever, is surrounded 
by air, or plunged in a fluid of a temperature lower than its 
own, it grows cooler, and finally assumes exactly the tempera- 
ture of the medium in which it is placed. In all cases, a body 
hotter than those which surround it, gives out to them its ex- 
cess of heat, until an equilibrium of temperature take place. 

When a body is placed in a vacuum, it still gives out its heat 
to the bodies which exclude the air, and finally, but more ra- 
pidly than before, comes to the same temperature with them. It 
is thus evident that the heat possessed by a body, even when 
isolated in an empty space, passes through that space to the 
surrounding bodies. This heat, which is thrown off from every 
point of a heated body, is said to Radiate. 

Heat radiates not only when the body is placed in vacuo, but 
when it is surrounded by air, by other gases, and by liquids. 
And it is sufficient for the present purpose to examine how the 
radiation is performed in air ; for not only are the experiments 
more easy than in a vacuum, but it is in this medium that ra- 
diation takes place most frequently. Air may diminish the in- 
tensity of the radiating heat, but does not alter the laws which it 
follows. 

Heat is thrown off by a heated body in right lined directions, 
as if it issued from the centre of a sphere in the direction of its 
radii. When thus radiating, it is capable of being reflected ; 
and this reflection takes place in the same manner as that of 
light ; that is to say, the angle of Reflection is equal to the an- 
gle of Incidence, and both are included in a plane perpendicu- 
lar to the reflecting surface. Polished surfaces reflect heat 
best ; and it has been found to be a general law, that the power 
both of absorbing and emitting heat from the surface of bodies, 
follows a common law, and is inversely proportioned to the 
power of reflection. The power of giving out heat is called 
that of radiating, and the experiments which have been made 
upon this property in bodies give the following proportional re- 
sults. 



2S 



PHYSICAL PRINCIPLES. 



Table of the Radiating Power of different Bodies. 



[— ^^— IMHJ "" ™" IM ■— ■■■■IIIIBM^ 


nf 


Lamp Black, ..... 


100 1 

100 


Water, ...... 


Writing Paper, . 


98 


Glass, ...... 


90 


India Ink, ...... 


88 


Ice, ...... 


85 


Mercury, ...... 


20 


Brilliant Lead, ..... 


19 


Polished Iron, ..... 


15 


Tin, Silver, Copper, .... 


12 


, 


1 



Of all substances examined, lamp black and water radiate 
best, and polished metals worst. When a metal is scratched or 
tarnished, or when it is covered with a coat of water, of var- 
nish, or even of woollen stuff, its power of radiation is increased. 

The inverse relation which takes place between the powers 
of reflection and absorption might be almost inferred without 
the aid of experiment ; for all the heat which falls upon a sur- 
face must be either reflected or absorbed ; the less, therefore, 
that is reflected, the more ought to be absorbed. The relation 
between the properties of radiation and reflection is not so ob- 
vious, but experiment shows, that as the one increases the other 
diminishes. 



18. When the temperature of a body differs from that of the 
surrounding medium, its mode of heating or cooling depends 
not only on its power of radiating, absorbing, and reflecting 
heat, but also upon the manner in which the heat it receives, 
or parts with, is distributed or withdrawn from its mass. No 
body permits radiating heat to penetrate to any great depth 
within its mass ; in solid bodies, any farther heating is due to 
the radiation among their particles. This propagation of heat 
among the particles of bodies is called their conducting power. 
Different bodies possess this property in very different degrees : 
thus, a rod of glass may be safely held close to the place where 
it is in actual fusion, and a piece of charcoal to the place where 



PHYSICAL PRINCIPLES. 



29 



it is burning ; while if a bar of iron be heated red hot at one 
end, the other is so much heated that it cannot be safely 
touched. 

Gold and silver are the best of all conductors, and all the 
metals are good conductors ; clay and pottery are much worse, 
and charcoal still more so. Straw, wool, cotton, down, and 
other substances of similar structure, are the worst conductors 
among solid bodies. This is, however, in a certain degree 
owing to the presence of air, which they confine in such a man- 
ner as to prevent its entering into circulation. Among the solid 
substances on which experiments have been made, the follow- 
ing relative powers of conducting heat have been observed. 

Table of the Conducting Power of different bodies. 



Gold, 
Silver, - 
Copper, 
Iron, 
Zinc, 
Tin, 
Lead, 
Marble, - 
Porcelain, ■ 
Fire Brick, 



Li 




19. Liquids are. in general, worse conductors than any solid 
bodies. Their temperatures are, notwithstanding, rapidly rais- 
ed by a proper application of heat. Thus, if a heated body be 
plunged in a liquid, the layers of the liquid immediately in con- 
tact with the body are heated ; they expand, and become speci- 
fically lighter than those which surround them ; they in conse- 
quence rise, and are replaced by others, which rise in their turn ; 
and the motion continues until the solid and the whole mass of 
liquid assume a common temperature. When the vessel that 
contains a liquid is heated from beneath, a double set of currents 
is formed, the one of the warmed particles which rise, and the 



30 PHYSICAL PRINCIPLES. 

other of cold, which descend to supply the place of the former. 
But if the heat be applied to the top of the fluid, no more than 
the upper surface is heated, and the rest retains its original tem- 
perature, or is warmed in a degree hardly perceptible. 

20. Gases are affected in the same manner, but, being less 
dense, they carry off, by their motions, less heat than liquids do ; 
and the radiation, which is hardly perceptible in a liquid body? 
becomes the most prominent cause of the cooling of a body ex- 
posed to the air. 

The rate of the cooling of a body, surrounded by a fluid medium, 
depends, then, as well upon its power of radiation, as upon the 
abstraction of heat by the motion of the particles of the medium. 
The quantity of radiation decreases in a geometric ratio as the 
temperatures are lessened in arithmetic proportion, and it de- 
pends upon the character of the surface of the body. The rate 
of cooling by the contact of a fluid is. on the other hand, inde- 
pendent of the nature of the surface ; but is most rapid from bo- 
dies which are themselves good conductors. Both the tempera- 
tures and the rate of cooling vary in a geometric ratio, but the 
common multiplier differs in the two progressions. In the tem- 
peratures it is 2, while in the rates of cooling it is 2.35. 

The cooling property of gases may always be expressed in 
terms of some power of their pressure. The coefficient of the 
power is, in air 0.45, in hydrogen 0.315, in carbonic acid 
0.517. 

These laws are directly applicable to masses of fluid bodies, 
because heat or its diminution is propagated in them with ex- 
treme rapidity by means of their internal motion. In solid 
bodies the communication of heat is more slow : but in both, 
the laws both of heating and cooling are identical. 

21. When a solid body is cooled, by being placed in a me- 
dium whose temperature remains constant, the outer part cools 
first, and the temperature increases from the surface to the 
centre ; but this difference gradually becomes less and less, and 
the whole will finally reach an uniform heat equal to that of 
the surrounding medium. 



PHYSICAL PRINCIPLES'. 31 

When a solid body is placed in a medium of higher tempera- 
ture than its own, the temperature will be at first greatest at 
the surface, and least in the centre ; but the heat will gradually 
penetrate, until the whole of the particles attain the heat of the 
surrounding mediums. 

When the solid is only heated at some one point of its sur- 
face, the remainder will receive heat by virtue of the conduct- 
ing power. But, as every point in the surface will radiate heat, 
it becomes obvious that a limit will be reached, when the quan- 
tity of heat lost by radiation will be exactly equal to that com- 
municated to the body. Thus the temperature will become 
constant, but each different point will have that which will de- 
pend upon its distance from the point to which the heat is di- 
rectly applied. 

If a solid body be formed into a vessel, and contain a liquid, 
and if heat be applied beneath, the motion of the liquid will 
bring all the parts, with which it is in contact, to its own tem- 
perature, which the interior of the vessel will not surpass. The 
outside of the vessel will have a temperature greater than the 
liquid it contains; and this difference will depend upon the con- 
ducting power of the material of which the vessel is formed. If 
this material be a bad conductor, the difference may be consider- 
able; but in metallic vessels, the difference will be hardly per- 
ceptible. If, on the other hand, the heat be applied above the 
surface of the liquid, the latter will no longer act to prevent this 
part of the vessel being heated as high as the substance that fur- 
nishes the heat is capable of doing. So also, if the heat be ap- 
plied below the surface, but near it, little or none of the heat 
will descend through the solid sides of the vessel. 

If, by any accident, a non-conducting substance be interposed 
between the vessel and the liquid, in this case also the vessel 
may acquire aheat greater than that of the liquid, and the heat 
will be distributed as if no liquid were present. 



CHAPTER II. 



COMBUSTION. 



Definition of Combustion. — Oxygen. — Flame. — Atmospheric 
Air. — Currents of Air -produced by Combustion. — Increase 
of Weight in the process of Combustion. — Temperature of 
Flame, and modes of burning of Solids, Gases, and Li- 
quids. — Different species of Fuel. — Properties and Chemi- 
cal Nature of Fuel. — Carbon and Hydrogen. — Compara- 
tive value of different kinds of Fuel. — Parts of Furnaces. — 
Ashpit. — Grate. — Body of the Furnace. — Flues. — Chim- 
neys. — Damper. — Furnace Doors. 

22. Of the various sources of heat, but one is of importance 
in its relation to our subject ; this is, the chemical process 
which is called Combustion. The process, in its general and 
most extended sense, denotes the combination of bodies with a 
class of simple substances, that are thence called Supporters of 
Combustion ; as applicable to our present object, it is restricted 
to their combinations with but one of them, namely, Oxygen. 

23. Oxygen is an insipid, colourless, ponderable body, which 
we find existing in nature in a gaseous state, and which pos- 
sesses the property of entering into combination with all well- 
known simple substances with a greater or less degree of ener- 
gy. These combinations are all attended with the develope- 
ment of a greater or less degree of heat, and the quantity of 
heat appears to be proportioned to the energy of the action by 
which the combination is effected. 



COMBUSTION. 33 

24. It is a general law, that all bodies when intensely heated, 
become luminous. When this heat is produced by combination 
with oxygen, they are said to be ignited ; and when the body 
heated by this chemical action is in a gaseous state, it forms 
what is called Flame. 

25. Oxygen is one of the principal constituent parts of atmo- 
spheric air, of which it forms about one-fifth part, and it is from 
the atmosphere that the oxygen, which is the agent in the com- 
bustions that we apply to generate artificial heat, is derived. 
Although it is thus absorbed from the atmosphere in large 
quantities, by processes both natural and artificial, it does not 
suffer diminution in quantity, for there are several natural ac- 
tions that are constantly restoring and replacing it. By a pe- 
culiar mechanical law that affects elastic bodies, they are uni- 
formly distributed over the surface of the earth, each acting as 
if it were a distinct atmosphere ; and hence the quantity of ox- 
ygen in the air is identical in all places and under all circum- 
stances. 

Not only is the quantity of heat developed by the combina- 
tion of different bodies with oxygen extremely variable, but 
that at which they begin to combine is also very different. 
There are some that unite with it at the ordinary temperature 
of the atmosphere, while others require to be previously subject- 
ed to the most intense heat we have the means of producing ; 
there are others again, with which it will only combine at the 
moment in which it is in the act of being separated from some 
of its other chemical combinations. 

26. As the oxygen forms, in the process of combustion, a 
combination with the combustible body, it is obvious that a giv- 
en quantity of atmospheric air must have its property of sup- 
porting combustion rapidly destroyed ; and hence whenever the 
process is intended to be continued, it is necessary to supply 
fresh masses of air. The very process itself is, however, capa- 
ble of creating currents in the atmosphere that will continue 
until a great part or the whole of the combustible has entered 
into combination ; and we may, by a skilful application of me- 
chanical principles, regulate and govern the supply of air thus 

5 



34 COMBUSTION. 

drawn towards the "burning body. In some cases, however, 
where intense heat is desired, it becomes necessary to urge, over 
the surface, or through the mass of the combustible, currents of 
air by mechanical means. Apparatus for this purpose are call- 
ed Blowing Machines, of which the common bellows is the most 
familiar instance. 

The currents that we have spoken of are formed upon the 
principle, by which, as we stated in the last chapter, bodies are 
cooled when placed in fluids. The oxygen generally enters 
into combination with the greater portion of our common fuel 
without losing its gaseous form ; and although more dense at a 
given temperature than it was before, it is generally so much 
heated as to become specifically lighter than the adjacent air, 
while the rest of the mass of air becomes equally heated, with- 
out undergoing any chemical change. Another of the combi- 
nations of oxygen with one of the constituents of our fuel is 
aqueous vapour, highly rarified by the heat of the combustion ; 
these t\vo> substances, therefore, rise along with the part of the 
air that has not entered into combination ; and the contiguous 
air rushes towards the burning body,, in order to supply the 
place of the rising column. Chimneys or flues are usually 
adapted to carry up the heated air. The draught of these is 
rendered more intense, by permitting no air to enter them but 
what passes through the fuel ; and the quantity that shall thus 
pass may be regulated, either by changing the magnitude of 
the opening by which the air enters the fire, or by varying the 
area of the flue. An apparatus intended to fulfil the former of 
these objects is called a Register, one to fulfil the latter, a 
Damper. 

27. Although the density of oxygen is by no means great, 
still, as it is ponderable, it must in all cases increase the weight 
of the combustible. This, at first sight, appears contrary to 
ordinary experience, which perceives bodies wasting and di- 
minishing under the process of combustion. This apparent 
anomaly grows out of the fact, that the products of the process 
are in many cases gaseous, and hence escape along with the 
current of air that passes through the burning body. Were we 



COMBUSTION. 35 

to collect the whole of the products, we should find in them an 
increase of weight exactly equal to that of the oxygen which 
has been consumed. 

28. Different bodies become luminous in the process of com* 
bustion at different temperatures, solids more early than gase- 
ous bodies. None appear to become visible, even in a faint 
light, below a temperature of about 870° of Fahrenheit. The 
light is at first of a dull red colour; as the temperature aug- 
ments, the light becomes more brilliant, and the body finally 
shines with an intense white light. Solid bodies may become 
luminous when heat is simply communicated to them, and 
without entering into combustion ; but gases are never luminous^ 
except while entering into combination. Liquids burn only by 
becoming volatile, and hence it is the aeriform matter that es- 
capes, and not the liquid itself that becomes luminous. 

When a combustible is solid, and so fixed as not to become 
volatile by the heat generated by its own combustion, it burns 
only at the surface, and the heat generated resides in the place 
where the combustion occurs, whence it is propagated to the 
surrounding bodies by radiation, or by their conducting power, 
except so much as is applied to heat the current of air that flows 
through the mass of burning fuel. But if the body be one that 
is capable of becoming gaseous at a temperature below that at 
which it ignites, the combustion takes place principally in the 
gaseous matter, extends into the column of rising air, and into 
the flue by which it is conveyed. The heat the vapours ac- 
quire in their combination with oxygen renders them lumi- 
nous, and it is far more intense than that found where the fuel 
is itself situated. Solids may become volatile either by the 
physical process of evaporation, or by their constituents enter- 
ing into new combinations, whose natural state is that of gas ; 
flame is the product of their combination with oxygen in either 
case. 

The brilliancy of a flame is no criterion of the intensity of its 
heat. The flame of the compound blowpipe, the most intense 
in heat of any that we can produce, is barely visible in the open 
day. Those flames are most brilliant in which a gas is concern- 



36 COMBUSTION. 

ed, that has a constituent capable of returning to the solid form 
during the process ; this being capable of becoming more lumi- 
nous at equal temperatures than gas, imparts this property to 
the flame of which it constitutes a part ; such is the cause of the 
intense brilliancy of the flame of carburetted hydrogen, in the 
form of oil and coal gas, or of its purer state, olefientgas. Flame 
may be cooled until the gas ceases to be luminous, or to unite 
with oxygen. This is done by bringing into contact with it a 
metallic body, or other good conductor ; in this case no fresh 
heat is generated in the current, which, therefore, no longer pro- 
duces any new calorific effect. 

Flame, as a general rule, is hollow; that is to say, the gase- 
ous matter combines with oxygen only at its surface, except 
under particular circumstances : thus, the cone of a candle or gas- 
light is luminous only at its surface, but when an inflammable gas 
is intimately mixed with oxygen, the whole inflames suddenly 
and explodes, and when currents of air are propelled violently into 
the body of the flame, the heat is more intense, and less of the fuel 
escapes unconsumed than in cases of ordinary draught ; the whole 
gaeous matter, too, may be consumed within a less space. This 
principle has been advantageously applied in this country to 
the boilers of several steam engines, where, as the space is limit- 
ed, a more complete combustion within it is desirable. For this 
purpose a fan wheel has been used, and with great advantage. 
A similar plan has been more recently introduced in England, 
in the boiler of a locomotive engine, and is employed in the 
locomotive engines on the Baltimore and Ohio rail-road, in 
which anthracite is used as fuel. 

The current of air which flows towards and through a mass 
of burning fuel, produces two effects, directly contrary to each 
other. While, on the one hand, the oxygen that is necessary 
for supporting the combustion, generates heat by entering into 
combination with the fuel ; on the other, the residue of the at- 
mospheric air, which constitutes four-fifths of the whole, carries 
off a part, greater or less, of the heat thus produced. The actual 
effect in heating depends upon the difference of these two effects, 
and is influenced by the relation between the mass of air and 
that of the combustible. When the area of the current of air is 



COMBUSTION. 37 

small when compared with the bulk of the combustible, as 
when it is directed through a tube of small diameter, the energy 
of the combustion is increased, and the flame is longer ; on the 
contrary, when the same quantity of air enters by a larger ori- 
fice, the flame diminishes in bulk, and may even be extinguish- 
ed by the second of the above-described actions. 

Although a body which continues solid during combustion 
burns only at the surface, the heat generated may be sufficiently 
intense to render the body luminous throughout ; on the other 
hand, it is only at the surface that the currents of heated gas 
which constitute flame become luminous, butthe solid matter con- 
veyed by, or in the act of deposition from such a current, will 
be luminous, whether at the surface or not. 

Such are the general principles of combustion, and such the 
nature of flame ; they cannot be more fully developed, except by 
considering the peculiar nature and mode of burning of the se- 
veral species of fuel in actual use. 

29. Of the different species of fuel, those which are more 
commonly employed in generating steam are : 

1. Pine Wood, 

2. Hard Wood, 

3. Bituminous Coal, 

4. Anthracite Coal. 

Each of these has its peculiar manner of burning ; and hence 
the furnaces or fire-places in which they are used must differ in 
form and arrangement, as ought the flues and chimneys by 
which the current of air that passes through them is carried 
off. 

30. The general properties of a good fuel are, that it should 
burn easily in atmospheric air, and that the heat generated by 
the combustion should be sufficient to keep it up until the 
whole is consumed. The heat is carried off from the fuel in 
three ways : 

1. By the current of heated air. 

2. By the direct radiation of its solid part; and, 

3. By the radiation of the flame that issues, and the conduct- 



38 COMBUSTION, 

ing power of the flues with which the flame comes into contact. 
In the application to the generation of steam, the first can be 
made but little use of, inasmuch as to cool this rising column 
of air would diminish its velocity, and thus lessen the draught 
of the chimney ; but both the kinds of radiation, as well as the 
action of conductors on the flame, should be employed, and the 
vertical part of the chimney should not commence except at 
the distance from the mass of fuel at which the flame termi-» 
nates. The simple combustibles which are found in the four 
different kinds of fuel which we have spoken of, are Carbon 
and Hydrogen ; the coals contain sulphur, but it is not, generally 
speaking, in sufficient quantity to affect the manner of their 
combustion. There is also present a portion of oxygen. 

31. Carbon is a substance which exists in a state nearly pure 
in common charcoal, and in the black deposit which is formed 
on the flues through which the column of air that has passed 
through burning fuel is carried. 

In these forms it is a solid body of a deep black colour, in- 
sipid and inodorous ; it is infusible by heat, and does not be- 
come volatile ; but in most species of fuel it is, during comhus- 
tion, divided into such small portions as to be readily carried 
off by the heated air, and is then deposited upon the flues, 
forming, with other condensed matter, Soot. 

It combines with oxygen in two different proportions, forming 
carbonic oxide and carbonic acid. The former still retains 
the property of combining with oxygen, and, as it is gaseous, 
forms flame, which has a pale blue colour ; the latter is incom- 
bustible, and extinguishes flame. 

Hydrogen, in its pure form, exists in a gaseous state, and is 
the lightest of all known substances, having a density of no 
more than one fifteenth part of that of common atmospheric 
air. It combines with half its bulk, or eight times its weight of 
oxygen, when inflamed ; and the compound that results is wa- 
ter, which, in consequence of the high heat generated by the 
combustion, is at first in a state of vapour. This combination is 
attended with the highest degree of heat ive can obtain by any 
combustion whatsoever, as is manifest from the effects of the 



COMBUSTION. 39 

compound blowpipe, in which an united stream of oxygen and 
hydrogen, in the proportions that constitute water, are inflamed. 

Hydrogen also unites with carbon, forming one well-known 
and universally admitted gaseous compound, Olefiant Gas. It 
is found also in the gaseous shape, containing a less proportion 
of carbon ; but it was, until lately, in dispute whether any of the 
various gases of this character be definite compounds, or sim- 
ply mechanical mixtures of olefiant gas with uncombined hy- 
drogen. The former opinion has at last prevailed. 

When a body, whether solid or liquid, which contains a 
combination of carbon and hydrogen, is exposed to a high heat, 
these gases are let loose and take fire ; other compounds, of 
which these two substances constitute an important part, are 
also sometimes generated, but which are not combustible. 

Thus, not only does a part of the fuel burn in the body of the 
furnace or fire-place, and its more volatile part separate, but new 
combinations take place there, a part of which are also inflamma- 
ble, and burn in the chimney if a sufficient quantity of un- 
combined oxygen enter it alon^ with them. These new in- 
flammable products are carbonic oxide and the carburetted 
hydrogens. 

32. Carbon, in burning, combines with no more than two 
and two-thirds of its weight of oxygen. In its combustion, one 
pound produces sufficient heat to increase the temperature of 
13000 lbs. of water 1° Fahrenheit. 

Hydrogen combines with eight times its weight of oxygen, 
and one pound of it, in burning, raises the heat of 420L0 lbs. 
of water 1°. 

Hence it is obvious, that of equal weights of fuel, that which 
contains most hydrogen ought in its combustion to produce 
the greatest quantity of heat. Such, in truth, is the case where 
the fuel is exposed, each kind under the most advantageous 
circumstances. And thus in steam engines pine wood is pre- 
ferred to hard, and bituminous coal to anthracite. But as hydro- 
gen, and the new compounds it forms, are easily separated in 
the form of gas, which also carries with it a dense smoke com- 
posed of minutely divided carbon, it is only when the whole 



40 COMBUSTION. 

smoke and gas can be consumed, that the species that abound 
in hydrogen manifest their full value. 

Li positions where the radiant heat of the fire-place can 
alone be made effective, or when the volatile matter either 
escapes unconsumed, or without being applied, those kinds of 
fuel which abound in carbon appear to be the most valuable. 
Thus, in the very careful and accurate experiments made by 
Marcus Bull, and published in the Transactions of the Ameri- 
can Philosophical Society, the values of the different kinds of fuel 
appear to be almost exactly in the ratio of the quantity of car- 
bon they contain. But, upon examination it will be found, that 
all the different substances were experimented upon in the 
same apparatus, and that one exactly suited to the most ad- 
vangeous combustion of charcoal and anthracite. His ex- 
periments are therefore no more than a comparison, and, no 
doubt, a valuable one, of the effects produced by the direct radia- 
tion of that part of the fuel which remains solid, and furnish 
no criterion of the absolute heating powers of the substances 
when each is burnt in a furnace of the construction best suited 
to its own mode of combustion. Charcoal and anthracite lose 
little or nothing in the form of smoke, and the carbonic oxide 
that is generated is generally completely burnt : this is not the 
case with any other species of fuel, unless burnt in apparatus 
expressly constructed for consuming smoke. We have felt it 
our duty to state our objections to the experiments of Mr-. Bull, 
as, in spite of these defects, they are the most valuable that we 
have it in our power to quote, especially as regards wood. 

When the hard woods, after being well dried, are subjected 
to destructive distillation, the residuum of solid charcoal is no 
more than one-fifth part of the weight 'of the wood. About 
one-fourth part of the volatile matter is condensible into the 
liquid form, being water charged with an empyreumatic oil 
and acetic acid, a mixture that usually goes by the name of 
pyrolignous acid. Full one-half of the mass goes off in a 
permanently elastic form. As analysis shows no other sub- 
stances present than the three we have stated, and as the oxy- 
gen is principally accounted for in the acid, these gaseous 



COMBUSTION. 41 

products are probably wholly inflammable. Pine wood fur- 
nishes little or no pyrolignous acid, and a less residue of char- 
coal ; hence we may infer that when it is well dried, full three- 
fourths of the whole weight are capable of forming flame. 

When wood is employed as a fuel, it ought to be as dry as 
possible. When recently cut, it always contains a considerable 
quantity of water ; and as in burning it does not acquire heat 
enough to decompose that fluid, the water must be converted 
into steam, which requires a considerable quantity of heat. 
Wood does not part with the whole of its moisture by mere ex- 
posure to the air, but retains at least one-tenth part of its weight, 
unless artificial heat, at least as great as that of boiling water, 
be applied. Hence, when wood is to produce the greatest 
quantity of heat which it is capable of affording, it ought not 
merely to be seasoned, but dried by the direct application of 
heat. As usually employed, it has about 25 per cent, of water 
mechanically combined, the whole of the heat necessary for 
evaporating which, is lost. 

Hard woods burn only at the surface ; the heat there gene- 
rated speedily causes the volatile matters of the whole mass to 
escape ; such of them as are inflammable take fire, and form a 
flame. There soon remains nothing but a compact, dense 
mass of charcoal, which burns slowly and without flame. 

Pine and other light woods burn with much more rapidity 
as they split under the action of heat, and are, besides, porous 
enough to permit the air to penetrate : much of the carbon too 
either assumes a new form of combination with the hydrogen, 
or is carried off in smoke ; they therefore leave little or no 
charcoal, and give out flame during nearly their whole com- 
bustion. 

The experiments of Count Rumford give the following re- 
sults : 



42 



COMBUSTION. 



Species of wood. 

Oak, seasoned, - 

dried on a stove, 

Maple, dried on a stove, 

Fir, seasoned, 

dried on a stove, - 



lbs. of water heated 
1° by 1 ib. of fuel, 

4590 
5940 
6480 
5466 
7150 



*a 



These are all too high for any practical purpose, as we rarely 
resort to artificial means of drying, and have but seldom the 
power of obtaining wood thoroughly seasoned. We therefore 
do not consider it safe to take at more than 4500 lbs. the quan- 
tity of water which 1 lb. of hard wood is capable of heating 1°, 
and 5000 for the quantity heated 1° by pine wood. 

The more useful of Mr. Bull's experiments upon wood are 
as follows, viz : 



I-"""""""" - *""""" 




"1 


Kind of Woods. 


Weight of 
Cord. 


Comp. value 1 
per Cord. |, 




lbs. 




Shell Bark Hickory, 


4469 


100 


Pig-nut Hickory, - 


4241 


95 I 


Red-heart Hickory, - 
White Oak, - - - 


3705 


81 


3821 


81 


Red Oak, - - - - 


3254 


69 


Hard Maple, - - 


2878 


60 


Jersey Pine, - - - 


2137 


54 


Pitch Pine, - - - 


1904 


43 


White Pine, - - - 


1868 


« 



The difference in the modes in which bituminous and an- 
thracite coal burn, is still more marked than between various 
kinds of wood. Those coals which contain much bitumen, (as 
Cannel coal,) burn much like pine wood, splitting and emitting 
an inflammable gas. Those which contain less, (as common 
Liverpool coal,) burn at first with flame, and then leave a mass 
of coke or charcoal, which burns without flame. Anthracite, 
on the other hand, has little or no flame, except what arises 
from the formation of a portion of carbonic oxide. All coals 
contain more or less water, but much heat is not lost in their 



COMBUSTION. 43 

combustion on this account. They do not burn, unless heated 
to a temperature at which water is decomposed, and in the 
flame that is formed, the two gases again combine and emit 
heat. On this account damp bituminous coal produces more 
flame than when it is dry ; and although it does not appear to be 
of any use to moisten the anthracites, those varieties which lie 
below the level of water in the mine are more easily ignited, and 
give more flame than those which are found in dry situations. 
When bituminous coal is subjected to the destructive distilla- 
tion, nearly two-thirds of its weight is left behind in the form 
of coke. This is principally composed of carbon ; a part of 
the volatile matter, although condensible, is inflammable, and 
will join in generating flame ; this, with the inflammable gases, 
amounts to about one-fourth of the weight of the coal, and the 
remainder, amounting to about -^j, is incombustible. 

The best anthracites contain about 95 per cent, of inflamma- 
ble matter, which is principally carbon. In burning them, how- 
ever, a very considerable residue of carbon is always left, as 
the interior of the pieces into which they are broken cannot 
be inflamed, and the dust does not burn. This is not the case 
with bituminous coal, which may have every particle exposed 
to the contact of air, by stirring it during combustion, and of 
which the smallest fragments inflame. If we calculate the 
heating powers of the two species of coal from their chemical 
composition, they will be as follows : 

a . „ f ,-,„„, Lbs. of water heated 1° 

Species of Coal. by 1 lb. of fuel. 

Average of bituminous coal, . . 1379?. 

Anthracite, ..... 12350 

Coke, - - - - . - 13000 

In practice, however, a considerable quantity of heat is wast- 
ed, which the best experiments make about one-third, in the 
case of bituminous coal and coke, and the loss in anthracite 
from its less perfect combustion must be even greater. 

The results thus reduced are, in the nearest round numbers, 

lbs. 

For bituminous Coal, - - - 9200 

For Coke, - - - • - - 8600 
For Anthracite, .... 7800 

but the latter is probably beyond the truth. 



44 



COMBUSTION. 



As a bushel of bituminous coal weighs from 80 to 84 pounds, 
and as the water which is used in feeding the boilers of steam 
engines has a temperature of 100°, the burning of a bushel of 
this coal is capable of converting 12 cubic feet of water into va- 
pour ; and the sum of the latent and sensible heat being a con- 
stant quantity, the result will be the same whether the boiler be 
employed to generate low or high steam. 

The relative values of different fuels may be ascertained by 
applying them to the decomposition of litharge. It is known 
from experiment, that pure carbon will reduce to the metallic 
form 34 times, and hydrogen 103,7 times, their own weights 
of that oxide of lead. This differs but little from the relation 
in their heating powers which has already been stated. Tak- 
ing these facts as the standard of comparison, we have the fol- 
lowing for the results of the latest experiments which have been 
made on this subject : 



Species of Fuel. 


Pts. of Litharge 
reduced. 


lbs. of water heated 
1° by 1 lb. of fuel. 


Oak seasoned, - 


12,5 


4790 


Do. artificially dried, 


14, 


5350 


Nut Wood, 


13,7 


5240 


White Pine, - 


13,7 


5240 


Yellow Pine, 


14,5 


5550 


Charcoal, 


25 to 32 




Turf, .... 


8 to 15 




Charred Turf, - 


17 to 26 




Lignite, .... 


17 to 27 


i 


Coal, Welsh, - - - 


31,2 


11,840 


Newcastle, 


30,9 


11,815 


Wigan, . 


28,3 


9820 


Belgium, ... 


29 


11,090 


Durham, 


31,6 


12,080 


Coke, good, 


28,5 


9910 


inferior, 


22,2 


7380 
11,090 1 
9560 J 


Anthracite, French, 


29 


Pennsylvania,* 


25 



33. The furnaces in which the fuel employed for generating 
steam is burnt, are composed of a chamber in which the com- 



COMBUSTION. 45 

bustible is placed, a grate on which it is laid, an opening 
through which the air enters to the fuel, and an ashpit, into 
which the unconsumed portions fall. Furnaces usually re- 
ceive the air from beneath and through the ashpit ; but in some 
cases the air descends to the burning fuel, and passes down- 
wards through the grate. In treating of these parts, we shall 
follow the air in its course, arranging them in the order in 
which it reaches them. 

34. The Ashpit is generally a quadrangular chamber enclos- 
ed on three of its sides by walls, and open on the fourth, which 
is surmounted by a bar of iron, or an arch. Its section is 
usually of the same size as the grate, and its height depends 
upon the circumstances of its position. It ought, however, to 
have an opening to the free air as large as the area of the grate. 
In engines placed on the land, it has lately been a practice, 
which is attended with advantage, to have a few inches of wa- 
ter at the bottom of the ashpit ; this is renewed by a small, but 
constant stream. The air that flows to the furnaces is thus 
kept cool, and enters them loaded with moisture, which in- 
creases the length of the flame. In some of the modern steam- 
boats the boilers are placed upon the wheel guards, and the 
space below the grate is open to the water beneath. The com- 
bustion is found in these cases to be more intense. There can 
be no other general rules laid down for the construction of the 
ashpit, which will naturally assume its form from the figure 
and size of the furnace, and the position in which it is to be 
placed. 

35. The grate is composed of parallel bars, usually of cast 
iron. They have frequently the form of a prism, whose section 
is an isosceles triangle, the base of which is uppermost. Their 
ends are rectangular, and wide enough to keep the triangular 
portions at a distance of half an inch. When long, they are 
made deeper in the middle, and gradually taper to their points 
of support. The size of the bars will depend upon their length, 
the weight of fuel they have to bear, and the shocks they are 
subject to in throwing it in and stirring it. The bars are 



48 COMBUSTION. 

usually about half au inch apart, and the bars of the largest 
furnaces an inch and a half thick. The open space through 
which the air passes, is therefore no more than a fourth part of 
the aperture on which the grate rests, and the space is farther 
diminished by the lodgment of the fuel upon, and the ashes and 
cinders between them. The least space that ought to be left 
for the passage of air through the grate should be equal to the 
area of the chimney, and the area of the grate itself is conse- 
quently four times as £reat. This, however, being the mini- 
mum, and the fuel and cinders opposing a resistance, grates 
ought always to be larger than four times the area of the chim- 
ney. We shall hereafter give the princples on which dimensions 
of this last-named part of the apparatus depend. It is usual 
among practical engineers to give a foot of area of grate for 
every cubic foot of water evaporated in an hour when the fuel 
is coals, and double that space when the fuel is wood. This 
rule agrees with that deduced from theoretic considerations by 
the French and German engineers. In practice, however, with 
any free burning fuel, it is better to have a surface of grate be- 
yond the absolute want, than one that may be too small. With 
anthracite, the case is probably different, as too large a column 
of air must diminish the intensity of the combustion. In the 
furnaces of Dr. Nott the bars are made extremely thin, and 
there is, in consequence, an obvious saving of heat. The open 
space is equal to that occupied by the bars. 

36. Above the grate is situated the body of the furnace. Its 
horizontal section is determined by the size and shape of the 
grate, its depth will depend upon the nature of the fuel. It 
must, in the first place, be of sufficient depth to allow such a 
thickness of fuel as is best suited to its complete combustion ; 
and in the second, there must be, above the fuel, a sufficient 
space for the flame to be fully formed before it enters into the 
flues. 

It is very difficult to state exactly a rule for the depth of 
the fuel that lies upon the grate. The larger the masses in 
which the fuel is thrown in, the greater may be its depth. 
The depth may also be increased with an increase in the 



COMBUSTION. 47 

draught of the chimney. In all cases, fuel may be added until 
it appears to diminish the intensity of the combustion ; for in 
this way the double advantage will be gained, of being compel- 
led to feed less frequently, and the air that enters will be more 
completely applied to the support of the fire. On the other hand, 
the quantity of fuel thrown on at one time must not be sufficient 
to deaden the flame, as in this case a great proportion of it will 
escape in the form of smoke. Wood requires to be most fre- 
quently added, and anthracite coal endures the longest. It has 
been found that a depth of about four inches is most advantageous 
for bituminous coal ; Anthracite will probably require at least 
double that depth, and wood will bear considerably more. In 
respect to the quantity of combustible, it is necessary that the 
furnace for burning wood should have at least twice the capacity 
of one for burning coal. A depth of from twelve to fifteen inches 
from the grate to the bottom of the boiler is sufficient for the 
most advantageous combustion of bituminous coal ; while it has 
been found in practice, that if the depth of the furnace, in which 
wood is burnt, be less than three feet, the useful effect of the 
fuel is lessened. 

When high steam is to be generated, the space may be made 
less, but it is in all cases disadvantageous to bring the boiler in- 
to contact with or too near to the fuel itself. The reason of these 
rules is obvious ; for if the heat be withdrawn immediately from 
the fuel itself, rather than from the flame and the heated air 
that has passed through the furnace, the volatile matter and 
heated air will cool too speedily, the length of the flame will be 
lessened, and much of combustible will escape unconsu med ; 
the draught of the chimney will also be diminished by the 
cooling of the air and the absence of flame. 

In respect to furnaces placed within the boiler, they at first 
sight appear to be extremely advantageous, because, as the 
boiler itself forms their enclosure, no heat can be lost. But this 
advantage is not real, for the surface of the furnace being cooled 
down by the water to a temperature which in low pressure boil- 
ers does not much exceed 212°, and, even in the case of high 
pressure, is far beneath the heat of flame, the combustion will 
languish, the draught of the chimney will be diminished, and 



48 COMBUSTION. 

the flame will be of but little length. On the other hand, it is 
frequently necessary to employ furnaces thus situated, in order 
to economise room and lessen the weight ; such is the case in 
steam-boats and locomotive engines. When such an arrange- 
ment becomes necessary, the inconveniences may be in some 
part obviated by lining the furnace with fire-brick, or other bad 
conductor of heat. The length of the flues may then be in- 
creased, and the whole gaseous matter converted into flame 
and applied usefully. 

There are cases in which it is of advantage to burn the 
smoke that issues from furnaces. As, however, when the fire 
is properly managed, but little unconsumed matter will issue 
from a furnace of the ordinary construction, such plans are of 
very little value in making the heat produced by a given quan- 
tity of fuel greater. It is only, then, when the smoke which 
occasionally issues, when fresh fuel is added, is productive of in- 
convenience to the neighbourhood, that furnaces of the kind 
need be erected, la a general treatise, therefore, it is not con- 
sidered necessary to enter into a detail of their construction. 

When bituminous coal is used as a fuel, it may be supplied, 
in proportion to its consumption, by a self-acting apparatus, the 
invention of Brunton of Birmingham in England. This is 
said to lessen the expenditure of fuel rather more than one-third. 
In our country bituminous coal is not yet much employed, and 
in consequence, we have not thought it necessary to describe 
the apparatus. Those who wish to become acquainted with its 
structure, may consult Tredgold and Lardner. 

37. From what has been already said, it will be obvious 
that the volatile parts of the fuel, and the heated air that has 
passed through it, are not to be permitted to enter at once into 
the chimney, but must be retained in contact with the boiler, at 
least until all the flame be made use of. The air and flame are 
therefore made to circulate in flues. These flues may be either 
beneath the boiler, upon its sides, or within it. Their length 
will depend upon the nature of the fuel ;. when it burns with 
much flame, they should be long ; but if it give but little, a horizon- 
tal passage beneath the boiler, and of its whole length, will be 



COMBUSTION. 49 

sufficient. Pine wood will therefore require the greatest length 
of flue, and anthracite coal the least. 

The greater the periphery of the flue under a given area, 
the greater will be the quantity of heat it will give out, but at 
the same time the greater will be the friction of the heated air 
against its surface. Here again a difference in form may arise 
according to the nature of the fuel ; the flues made use of, with 
combustibles that furnish the greatest quantity of flame, having 
the greatest practicable periphery, while those that burn with 
little or no flame should be square or circular. This, however, 
applies only to flues beneath the boiler or upon its sides ; for 
when the flues pass through the boiler, considerations of safety 
will generally require their section to be circular. 

Air being a bad conductor of heat, the bottom of a flue is 
less heated than its sides, and the latter much less than its top. 
Hence flues beneath the boiler are far more advantageous 
than those which surround it, and when a flue passes through 
a boiler, it ought, were there no other reason, to be entirely im- 
mersed in water. 

The whole area of the flues must not be less than that of 
the chimney, otherwise the draught will be impeded ; and, on 
the other hand, there is no advantage gained by making it 
greater. 

38. When the flame is completely expended, no farther ad- 
vantage is usually gained by making the current of air to circu- 
late in contact with the boiler. A part of its heat might, no 
doubt, be withdrawn, but this will be done at the expense of 
the intensity of the combustion, unless it be practicable to make 
the chimney of very great height. The ascent of smoke in 
chimneys is due to the difference in the density of the heated 
air they contain, and of that of the open atmosphere. The force 
which propels the current is, therefore, the difference of weight 
of two columns, one of atmospheric air, the other of the heated 
and rarified air of the chimney, whose altitudes are equal, and 
the same as that of the chimney, and whose areas are equal to 
that of the aperture by which the heated air enters the chim- 
ney. When, therefore, it is possible to make the chimney high, 

7 



50 COMBUSTION. 

the air within it need not be as much rarified, in order to ob- 
tain an equal force of draught, and the flues may be permitted 
to circulate longer around the boiler. We conceive, however, 
that it may safely be taken as a general rule, that when the 
gas has been wholly inflamed, the heated air may be permitted 
to ascend. In furnaces for burning wood and bituminous coal, 
it frequently happens that the flame enters the vertical chimney, 
and that much heat is lost ; while in those for burning anthra- 
cite, the flues are frequently so long as to diminish the draught 
of the chimney and the consequent intensity of the flame. 

The ascent of the air in chimneys is due, as we have stated, 
to their height and the temperature of the ascending column of 
air. But the latter is the mean temperature of the air in the 
chimney, and not that at which it enters. The sides of the 
chimney absorb heat, and it is again withdrawn from them by 
radiation, and the cooling action of the air ; and hence the ve- 
locity is rapidly diminished. Air, too, is subject to a considera- 
ble degree of friction in the chimney. 

This last resistance is proportioned to the square of the velo- 
city and the length of the chimney directly, and the diameter 
inversely. 

The cooling of the air depends not only upon the quantity 
of surface exposed, but upon the nature of the material ; and 
hence experiment alone can determine the effect which this has 
upon the velocity. We are aware that the greatest part of the 
heat that is thus lost is due to radiation. Now, of the materials 
usually employed in making the chimneys of steam engines, 
sheet iron, wrought iron, and brick, the first is the worst and 
the last the best radiator of heat. But the difference in this re- 
spect between the two first is but small, and as cast iron pipes 
must be thicker than those of wrought iron, the outer or radiat- 
ing surface of the former will be the least heated. Hence it 
would be reasonable to conclude that chimneys of cast iron 
have the best draught, those of brick the worst. This has 
been found to coincide with actual experiment. 

It has also been found that the friction of air in chimneys of 
different materials is not the same, that in brick being greatest, 
and in cast iron least. 



COMBUSTION. 51 

It is extremely difficult to calculate the proper dimensions 
for a chimney, inasmuch as many of the elements are difficult 
to determine. Peclet has given a method founded upon strict- 
ly scientific principles, but it is altogether too complex for prac- 
tice. The rule given by Tredgold, is — " Multiply the num- 
ber of cubic feet of water to be evaporated per hour by 112, 
and divide by the square root of the height of the chimney." 

This may be taken as the minimum for chimneys of brick, 
and with bituminous coal for the fuel. The last-named au- 
thor advises that the area of the chimney be made twice as 
much as is given by his rule. In chimneys of iron the area 
may be less, the fuel remaining the same ; and they may be 
still fulher lessened when the fuel is anthracite coal : on the 
other hand, the area of chimneys for burning wood should be 
greater than those for bituminous coal. The best form for the 
horizontal section of a chimney is that of a circle, for the fric- 
tion is less in it than ill any other figure, and in metal the cost 
of constructing it is also less. Of figures having circular sec- 
tions, the best is the frustum of a cone, whose upper area is 
that which is given by the rule of Tredgold, and whose lower 
section has twice that area. Tf the chimney be cylindrical, a 
small truncated cone or conoid, placed upon its top, will make 
it act more advantageously. 

39. As various circumstances will occur, in consequence of 
which it may be necessary to alter the intensity of the combus- 
tion, it is customary in most cases to place a Damper at the 
junction of the flues with the chimney. This is a plate of iron 
which slides in a groove, and may either wholly or partially 
close the aperture of the chimney. Its effect will be obvious 
from what has been stated of the draught of chimneys, which 
depends upon their height and the area of the space at which 
the smoke enters, as well as upon the difference of temperature 
of the external and internal air. In speaking of boilers, a me- 
thod of making Dampers self-acting, so as to close or open the 
aperture of the chimney in exact proportion to the heat which 
is required, will be mentioned. 



58 COMBUSTION. 

40. It remains to speak of the doors of furnaces. Those are 
usually rectangular, with hinges, and are fastened by latches. 
The material is generally cast iron, in some cases cast with a 
flaunch within, to support a lining of fire brick. The best of all 
would be a double door of iron, that when shut would enelose 
a stratum of air ; but the inner shutter would be too liable to be 
destroyed by the fire. 

When cleanness and neatness are desired, the whole front of 
the furnace is made of cast iron, with apertures for the doors 
and ashpit. In reverberatory furnaces, it is frequently usual to 
suspend the doors by a lever, to the opposite end of which is at- 
tached a counterpoise. Such an arrangement might probably be 
applied with advantage to the furnaces of steam engines. 

The form, arrangement, and distribution of furnaces, flues, and 
chimneys, depend, in a great degree, upon those of the boiler. 
Instances of those that are found to answer best in practice, 
therefore, cannot be given until the structure of boilers has 
been examined. 



CHAPTER III. 



BOILERS. 



Materials of which Boilers are constructed. — Figure of Boil- 
ers. — Strength and Thickness of Boilers. — Apparatus for 
showing the level of the water. — Feeding Apparatus. — 
Proof of Boilers. — Safety- Valves. — Air- Valves. — Steam 
Ouages. — Self-regulating Damper. — Common Damper 
and Register. — Dangers arising from the fire-surf ace be- 
coming bare of water. — Thermometer. — Plates of fusible 
metal. — Valves opening at the limit of temperature. — De- 
posits of solid matter, and modes of lessening and remov- 
ing them. — Steam-pipes. — Generator of Perkins. 

41. Water is converted into vapour, for the purpose of set- 
ting steam engines in action, in vessels that are called Boilers. 
These are always of metal, and three different materials are in 
use for their construction : Wrought Iron, Cast Iron, and Cop- 
per. Wrought iron and copper are rolled for this purpose into 
plates and sheets, which, after being bent to the proper form, 
are united by bolts, driven through holes punched around their 
edges, and riveted. When cast iron is used for boilers, they 
may either be of a single piece, or it may be cast in separate 
portions, which are united by screw bolts and nuts, passing 
through holes left or drilled in flaunches. Of the two first, 
copper is most easily worked, but it is far the most expen- 
sive material, and is therefore now used only in a few instan- 
ces, where the others are, from the circumstances of the case, 
inadmissible. Copper is much less easily acted upon by oxy- 
gen than sheet iron, and does not decompose water at any 



54 BOILERS. 

temperature ; it acts less powerfully upon the saline deposits 
that occur when sea or other impure water is used ; in ad- 
dition, it is less liable, than either of the other materials, to split 
or crack on sudden changes of temperature. 

Sheet iron is more tenacious than copper, but is liable to 
rapid oxidation, and has frequently invisible joints arising from 
the manner in which it is manufactured. Still, however, when 
the water used is tolerably pure, it is the best material, if we 
take into view the strength and comparative cheapness. 

The tenacity of copper is diminished by heat, but that of 
wrought iron increases up to the highest temperature to which 
it will in any likelihood be exposed in a boiler. 

The relative cost of boilers of the several materials may be 
estimated as follows : The comparative thicknesses of boilers 
to bear the same strain, are, 

For Copper, - - - 3 
For Sheet Iron, 2 

For Cast Iron, - - - 12 

The cost of them per lb. in New- York, is 

Copper, 34 cts. 

Sheet Iron, - . 16 " 

Cast Iron, - - - 6 " 

Their respective densities according to the table §9. 

Copper, - . - 8.878 
Sheet Iron, - - 7.788 

Cast Iron, - 7.207 

The product of these three elements give their relative cost 
as follows : 

Copper, 906 

Sheet Iron, 250 

Cast Iron, ----- 522 

Or, taking Sheet Iron as the unit : 

Copper, - - - . - 3.60 
Sheet Iron, - - - - 1.00 
Cast Iron, 2.09 



BOILERS. 55 

There is another point of view under which they ought to be 
examined, which is, the value of the material after the boiler 
has become unfit for service ; and here copper might appear 
to have the advantage, as it will sell for a far higher propor- 
tionate price than either of the others ; but still its depreciation 
in value, added to the interest on its cost, will be at least equal 
to the loss upon a boiler of wrought iron. 

42. In determining the proper figure of Boilers, various cir- 
cumstances appear at first sight as necessary to be taken into 
view. 1. The power to generate steam ; 2. The action of 
their own weight to change their figure ; 3. The pressure of 
the contained fluid ; 4. The action of the steam to burst them. 
Upon a more close investigation, it will, however, appear, that 
none of these, except the last, is of any real importance. 

The power of a boiler to generate steam depends upon the 
quantity of surface that is exposed to heat, and so long as this 
is the same, neither the figure of the boiler, nor the quantity of 
water it contains, have any effect upon its action. 

Boilers are liable to bend by their own weight, but to give the 
top the figure of an arch, and to support the boiler well from be- 
neath, obviates all difficulty on this score, except in boilers of the 
largest kind ; and the most brittle of the three materials has in this 
respect an advantage over those which are more flexible. The 
pressure of the contained water also acts to change the shape of 
a boiler ; as this force depends upon the product of the surface 
by the depth of the liquid, it increases with the height the 
liquid stands in the vessel, and with the developement of its 
sides ; aud under equal depths, a vessel whose section is a cir- 
cle will sustain the least pressure. Both of these actions may 
be rendered of little amount by distributing the water in several 
boilers instead of increasing the size of a single one. 

Neither of these influences can be compared in their amount 
to the strain exerted by the steam which is generated within 
the boiler. This, too, varies in different species of engines. 
In some, as we shall see, the steam is condensed, and that flow- 
ing from the boiler acts against the partial vacuum which is 
thus formed. The steam in this case need not have an expan- 



56 BOILERS. 

sive force of more intensity than the pressure of the atmosphere, 
and it sometimes does not exceed that limit by more than a 
few inches of mercury ; such engines are called Low Pressure. 
There are, however, some condensing engines to which the 
names of Low Pressure is improperly applied, as means have 
been found to use, and condense steam of a tension of several 
atmospheres. Instead, therefore, of distinguishing engines as of 
high or low pressure, we shall speak of them as condensing, 
or high pressure, and with the former, steam of medium, or even 
high pressure, is frequently used. In other engines, which are 
called High Pressure, the steam employed never has an elastic 
force less than two atmospheres, more frequently reaches four or 
five, and sometimes is as great as ten. Boilers of the first descrip- 
tion do not usually require materials of any great strength, nor 
is it necessary in them to seek for the form of greatest resist- 
ance. But in high pressure boilers, it is of the utmost import- 
ance, not only to use a material of sufficient tenacity, but to 
give them the figure which will be the least liable to yield un- 
der the great expansive force to which it is subjected. 

That figure which has the greatest strength to resist suchan 
expausive force, is one all of whose sections are circular. A 
sphere is the only solid which has this property, and it may be 
advantageously used upon a small scale. It, however, presents 
too small a surface, must have all its dimensions increased 
equally, and is not adapted to receive flues to retain the flame ; 
it is therefore never employed for the boilers of steam engines. 

All the sections of a cylinder at right angles to its axis are 
also circular, it therefore presents the greatest resistance to for- 
ces acting against these sections ; its ends, however, if plane 
surfaces, are comparatively weak. In Europe, where such 
boilers are of recent introduction, the ends are made of the 
same material with the body of the cylinder, and are formed 
into the shape of a portion of a sphere. In this country, where 
they have been long in general use, the body of the boilers is 
made of sheet iron, and the ends are plane surfaces of cast 
iron, made thick enough to be of equal strength with the other 
material, and firmly bolted to it. 

The same law that affects the strength of a vessel to bear an 



BOILERS. 57 

internal expansive force, also regulates its resistance to a pres- 
sure from without. Hence, spherical and cylindric boilers re- 
sist collapse, from the condensation of the steam they contain, 
better than those of other figures ; and hence also, when flues 
pass through boilers, they should be cylindrical. 

From what has been said §30. in speaking of the action of 
fuel, it will be obvious that the heat penetrates into the boiler 
by radiation from the burning mass, or by the direct contact of 
the flame and hot air with its surface. The exterior face of 
the boiler first receives the heat, it is then propagated in the 
metal by its conducting power, and the latter heats the water 
in contact with its interior, by causing a motion among its par- 
ticles. It is clear, then, that the quantity of water in the boiler 
has no influence on the quantity of steam which can be formed 
in a given time. All that is necessary is, that there should be 
enough to cover the whole metallic surface, to the outside of 
which the heat is applied. Hence the quantity of fuel con- 
sumed, the extent of the heated surface of the boiler, and trie 
conducting power of the substance of which it is made, are the 
only elements that need enter into the calculation of the quan- 
tity of steam a given boiler will generate. It is better, too, to 
depend upon actual experiment for the effect, than to deduce it 
from any theoretic considerations. From a mean of several 
such experiments, it has been deduced that six feet of fire sur- 
face are sufficient to evaporate a cubic foot of water per hour. 
But as the flues will communicate less heat in proportion as 
they recede from the furnace, the sum of the surfaces of fur- 
nace and flues ought to be eight feet for each cubic foot of 
water to be evaporated per hour, for low steam, and for high 
steam, not exceeding five atmospheres, nine feet. 

As the quantity of steam generated, depends, then, wholly 
upon the extent of the surface of the boiler which is exposed to 
heat, and as the saving of weight is in many cases advantage- 
ous, it has been proposed to use a combination of tubes for boil- 
ers, which will expose a much greater surface, in comparison 
with their internal capacity, than larger cylinders ; for it is a 
mathematical law, that while the surfaces of cylinders of equal 
.ength increase as the diameters simply, their internal capacity 

8 



58 BOILERS. 

increases with the squares of that dimension. A saving may 
also be made in the material of which the tubes are constructed, 
for the strength of a metallic tube to resist an effort to burst it, 
increases in the inverse ratio of its diameter. It has also been 
proposed to immerse such tubes wholly in the flame, and inject 
into them from time to time a certain quantity of water, to be 
converted almost instantly and wholly into steam. 

The first of these plans has a speedy limit in practice, and 
the last is wholly inadmissible, as will appear from the follow- 
ing considerations. 

1. The presence of a conducting body in the midst of 
the flame, will cool the gas of which it is composed, diminish 
the intensity of the combustion and the draught of the 
chimney. 

2. When tubes are actually heated to the proper degree, 
and no longer act to cool the flame, the flues must be made 
short enough to permit the air to enter the chimney as soon 
as it is cooled down to the temperature of the tubes ; other- 
wise, instead of heating them farther, it will tend to cool them. 

In tubular boilers, also, the generation of steam will be at 
first extremely rapid, and will displace the water they contain ; 
the quantity of steam generated will then diminish, and the me- 
tal being no longer cooled by contact with the liquid, will be- 
come red hot. Various inconveniences, which will be referred 
to hereafter, will arise in consequence. 

3. The principal objection to the last plan is founded upon a 
remarkable experiment of Klaproth, which is as follows, viz. 
If a polished spoon of iron be taken and heated to a white 
heat, and a drop of water be let fall upon it, the drop divides at 
first into several smaller ones, which, however, speedily unite. 
This, if it be closely observed, will be seen to have acquired a 
rotary motion : it continually decreases in bulk, and finally 
explodes. A second, and a third drop exhibit the same phe- 
nomena, but the continuance of the drop upon the metal be- 
comes less and less as the latter cools. One of the experiments 
gave the following results ; and the others, although the abso- 
lute times of duration differed, all exhibited a similar law. 



BOILERS. 




The first drop remained 


40" 


The second, - 


- 20" 


The third, 


6" 


The fourth, - 


- 4" 


The fifth, - 


2" 


The sixth, - 


- 0" 



59 



This experiment of Klaproth has been confirmed by others 
of greater accuracy, made by a committee of the Franklin Insti- 
tute. In these experiments it was found, that the evaporating 
power of iron increased up to the temperature of 334° ; that 
the decrease in the evaporating power was so great above that 
limit, that the quantity of water which was evaporated at that 
temperature in 1", required 15 seconds for its evaporation at 
395°. 

Perkins observed similar phenomena in the generator of his 
engine. This vessel being heated red hot, while empty, water 
was admitted. The elastic force of the vapour was at first but 
small, and increased rapidly as the temperature of the generator 
was diminished. 

The explanation which has been given of this phenomenon 
is as follows, viz. when it occurs, the water is never in con- 
tact with the metal, or at least only at a single point, as is 
shown by the spherical figure of the drops, and their rotary 
motion ; a stratum of steam intervenes, which, being a bad con- 
ductor, does not convey heat to the drop ; and the expansion 
of the drop, out of contact with the metal, appears to be due to 
a repulsion which is exerted by incandescent bodies upon 
those which are colder. This last explanation is corroborated 
by another curious fact observed by Perkins. He adapted to 
his generator, by an aperture of one-eighth of an inch in diame- 
ter, a tube or adjutage of three feet in length and half an inch in di- 
ameter within ; this tube was closed by a stop-cock, and the safe- 
ty valve loaded with a weight of about 700 lbs. per square inch. 
The generator being heated red hot, the steam contained in it 
opened the safety valve ; but, although the cock of the adjutage- 
was opened, no steam escaped by it until the temperature was 
considerably lowered. 

Thus it appears that the rapidity of the evaporation does not 



60 BOILERS. 

increase with the temperature of the vessel into which the wa- 
ter is introduced. It probably does so as long as the water is ca- 
pable of moistening the metal, which it can only do before that 
becomes incandescent ; but after the metal reaches a red heat, 
the rapidity of the evaporation decreases with every increment of 
heat. 

Tubes, or other vessels, into which the water is injected and 
thus converted into steam, have this additional disadvantage : 
the deposits of solid matter that fall from almost all water when 
evaporated, and which are greater in proportion as the water is 
impure, become harder and more compact than when the boil- 
er is kept full of water ; they also adhere more forcibly to the 
metal, and are more liable to corrode it. 

The objections which have been stated to tubular boilers do 
not apply to the use of tubes for conveying flame and heated 
air, from the furnace to the chimney. The latter method has 
now come into universal use in locomotive engines, and has 
been applied advantageously in steam-boats. It ought, howev- 
er, to be observed, that they are generally placed too near each 
other, and that the space for water between them may thus be so 
far diminished as to render the boiler liable to the same objec- 
tions as if it were itself tubular. This remark is more particu- 
larly applicable to the tubular flues which are situated near the 
bottom of the boiler. 

A boiler has been used for some years in England in experi- 
ments on carriages intended to be moved by steam on common 
roads. This is the invention of Hancock. It is composed of a 
number of rectangular cases proceeding downwards from a com- 
mon reservoir. These are sustained by bars of iron interposed 
between them, which divide the intervening spaces into rec- 
tangular flues. The whole is bolted together by rods, which 
traverse both the spaces which contain water, and the iron bars. 
Such a boiler will possess great strength, and will expose a 
great fire surface in proportion to its capacity. It is, however, 
obvious, that if the dimensions of the rectangular cases be too 
much diminished, the arrangement will be liable to the same 
difficulties which attend the use of tubular boilers. 

It has been proposed in this country, and we have seen it 



BOILERS. 61 

practised in several cases, to adapt to the lower part of boilers, 
tubes communicating with them, and immersed in the flame. 
Saqh, too, was the form proposed by Woolf in England. Ac- 
tual experiment has shown that such an addition has no real 
advantage, and when the tubes are constructed of cast iron, 
they run the risk of being broken by the sudden variations in 
temperature to which they are exposed. It may therefore be 
inferred as a general rule, that it is better to use cylindrical 
boilers of at least a foot in diameter, than tubes of small size, 
whether alone, or communicating with larger vessels. 

43. We have stated that the most important force to which 
boilers, and particularly those containing high steam, are expos- 
ed, is the expansive energy of the steam itself. The action of 
this force upon the sides of a cylinder is proportioned to the 
elastic energy of the steam, and the radius of the cylinder ; and 
it is resisted by the cohesive force of the metal. 

If the ends be a portion of a sphere whose radius is equal 
to the diameter of the cylinder ; then the strain upon any giv- 
en surface is equal to that upon the sides. 

When the ends, as is usual in this country, are plates of cast 
iron, their strength is investigated upon the principle of a beam, 
equally loaded throughout its length, and supported at the ends. 
The force that will break it, is proportioned to the square root 
of the pressure, multiplied by the square of the diameter. 

The absolute weight which a cubic inch of the usual mate- 
rials will bear without breaking, is, for 

lbs. 

Bar Iron, - 64000 

Sheet Iron, - 57000 

Cast Iron, .... 19000 

Sheet Copper, - - - 40000 

It is not, however, sufficient that the boiler shall not break 
under the expansive force ; it must not even change its figure 
nor must the bolts, by which it is fastened, give. These ma- 
terials are, in consequence, much nearer in value than their ab 



62 BOILERS. 

solute strengths would show ; for cast iron will bear 153001b§. 
per cubic inch without changing its shape, and wrought iron 
no more than 178001bs. 

The change of figure that each will support without break- 
ing, is also very different ; in cast iron, the limits of expansion 
and fracture are very near to each other ; sheet iron will 
stretch before breaking from - 1 - to -/-„- ; while copper may be 
expanded f ths of its original dimensions. Another circumstance 
also must be taken into account, which is their respective lia- 
bilities to break by sudden changes of temperature ; to this cast 
iron is very liable, sheet iron but little, and copper not at all. 
Taking all these circumstances into account, we have assumed 
as the numbers proper to represent the strength of these mate- 
rials, 

lbs. 

Sheet Iron, - 9000 

Copper, .... 6000 

Cast Iron, - 3000 

The first being about half the strain that wrought iron bears 
without changing its figure ; the other two bearing the nearest 
ratio to it in round numbers, that their respective strengths do. 

It is also to be taken into view, that the tenacities first given, 
are estimated from experiments made upon the metals when 
cold, while it may occasionally happen that parts of the boiler 
reach a red heat. Now, it has been found from actual experiments 
that the tenacity of copper and cast iron may be diminished, by 
heating them red hot, to not more than a sixth-part of that which 
they possess at an ordinary temperature. The numbers last 
given are reduced from the first in even a greater ratio, and there- 
fore are sufficiently small to make full allowances for this de- 
crease of strength. On the other hand, it appears from experi- 
ments performed at the Franklin Institute, that the tenacity of 
wrought iron is increased by heat. 

The usual rule for estimating the thickness of the plates of 
which cylindrical bodies are made, is as follows : 

Multiply the Radius in inches by the pressure on each 



BOILERS. 



63 



square inch in lbs. and divide the product by the number as- 
sumed above as the strength of the material, the quotient is 
the thickness hi inches. 

The rule for the ends is as follows : 

If of the same material with the body of the cylinder, the 
ends, if hemispherical, need only be half as thick ; if a por- 
tion oj a sphere, whose radius is equal to the diameter of the 
cylinder, the two thicknesses are equal. If of any other ra- 
dius, multiply half the radius in inches by the pressure in lbs. 
and divide by the cohesive force of the material. 

If the ends be plates of cast iron, 

Multiply the pressure on each square inch in lbs. by the 
square of the diameter in inches, and divide the product by 
twice the cohesive force of the material, the square root of the 
quotient is the thickness in inches. 

Such are the rules which theoretic considerations would 
point out. We shall proceed to compare their results for a 
pressure of lOOlbs. per square inch, with the practice of the best 
engineers of this country, in cylindric boilers of sheet iron with 
cast iron heads. 



r= 



_, 



Diameter of 


Thickness nf 
Sheet Iron. 


Thickness of 
Cast Iron Heads. 


Cylinder. 


Calculated. 


Used. 


Calculated. 


Used. 


in. 

IS 


in. 

0.1000 


in. 

0.1875 




in. 
1. 


24 


0.1333 


0.1875 




1.25 


30 


0.1667 


0.250 




1.25 


36 


0.2000 


0.250 




1.50 


42 


0.2333 


0.250 




1.50 



The labour of bending and shaping thick boiler plate is so 
great, and the imperfections of sheet iron increase so rapidly 
with its thickness, that, as a general rule, it may be stated that 
the diameter of cylindrical boilers, for high pressure steam, 
should not exceed 30 inches. There are, however, exceptions 
to this rule, in the cases of steamboats and locomotive engines 
where it is usual to carry the flues through the boiler. 



64 BOILERS. 

When fines are thus situated, the same reason that leads to a 
preference of cylindrical boilers, would point out that the form 
of the flues should be of that figure. The same rules may be 
adopted for estimating their thickness. In all other cases it is 
better to increase the number of boilers, than to increase their 
diameter. 

An increase in the number of boilers rather than an increase 
in the diameter of a single one, has this farther advantage, that 
the weight of water will be much less in the former than in the 
latter case. In increasing the diameter, the quantity of water, 
(the length of the cylinder remaining the same,) will increase 
with the square of the diameter, while the surface exposed to 
heat only increases as the diameter simply. A cylinder of 
twice the diameter will therefore carry twice as much water as 
two separate cjdinders, while it has only the same capacity for 
generating steam. From what lias been said, it may be infer- 
red that sheet iron is the best material, and a cylinder the best 
shape for boilers in all usual cases. When sea water is used, 
copper is, however, the only one of the three materials that can 
be depended upon to resist the action of the saline deposit. 
In condensing engines, the cylindrical form has rarely been 
used, although it has advantages even in this case. But in 
Cornwall (England), in the engines employed in draining mines, 
cylindrical boilers containing cylindrical flues have taken the 
place of all others. The original boiler of Watt and Bolton 
had its vertical section constructed upon a rectangle, by describ- 
ing a semicircular arc upon its upper side, forming a convex 
arch, and three less circular arcs within the remaining three 
sides, forming curves concave to the exterior. The lower arc 
is exposed to the fire, the two on the sides afford space for the 
return flues on the outside of the boiler, ^ee PI. L, Fig. 2. 

This form of boiler is only to be found with engines of an- 
tient date, and has given birth to a variety of others. In the 
boilers intended for steam-boats the fire-place was formed by 
extending the boiler downwards so as to form three sides 
both of the furnace and ashpit, and the return flues were carried 
through the boiler. The fire surface was increased by mamil- 
lary projections, called teats ; and finally, the direct flue was re- 



fiOILEftS; 65 

placed by a great number of small tubes. This form, which 
has as yet been chiefly applied to locomotive engines, and the 
invention of which is disputed by France, England, and the 
United States, is the most advantageous of any yet attempted* 

44. When boilers have been filled to the proper height with 
water, they will require a supply equivalent to the quantity of 
liquid that is carried off in the form of steam* This supply 
maybe either admitted from time to time by the engineer when 
the water has fallen to a certain conventional level, or it may 
be introduced by a self-acting apparatus in such a manner as to 
keep the wate* at a constant height. 

In the first case it is indispensable that the fireman or engi- 
neer should have it in his power, at any instant, to determine 
the height at which the water stands in the boiler ; and al- 
though the apparatus for this purpose is not indispensable when 
the boiler is supplied by one that depends for its action upon the 
state of the water itself, it is so valuable a check upon the opera- 
tion of the supply, that it should be adapted to all boilers. 

The most usual and most ancient contrivance for this pur- 
pose, consists simply of two stop cocks; each of these is attach- 
ed to a short tube ; one of them communicates with the boiler 
below the level at which it is wished to retain the water, the 
other enters it above that height. If the former of these be 
opened, and steam issue, water must be immediately supplied ; 
if the latter give out water, the Jiquid stands too high. These 
tubes, in boilers where the steam has an elastic force little ex- 
ceeding the pressure of the atmosphere, must be introduced hori- 
zontally into the sides of the boiler ; but where high steam is 
used, they may rise vertically through its top, and be afterwards 
bent in a horizontal direction. Although two such stop-cocks 
are sufficient, a third is usually placed halfway between them* 
In their use, one precaution is necessary, namely, to leave them 
open long enough for the water which may have condensed in 
them to be blown out. See PI. I., Fig. 5 and 6. 

The best apparatus for ascertaining the level of water in a 
boiler, is a straight glass tube, open at both ends, which are plac- 
ed in two cups that communicate by means of tubes with the 

9 



66 BOILERS. 

interior of the boiler. To these cups the tube is cemented, and 
the water will stand in it at the same height that it does in the 
boiler. It was at one time supposed that this simple method 
could not be adapted either to high pressure boilers, or to those 
made of materials other than copper, but it has of late been suc- 
cessfully introduced in both cases. 

Another mode, which, however, has rarely been used with 
steam engines, is to adapt a tube, made like the pipe of an or- 
gan, to the boiler, the lower end of which descends as far as 
the level, below which the water ought not to be permitted to 
fall. So soon as the water decends the least space below this point, 
steam will escape through the pipe, and give warning of the 
necessity for a supply by the sound it causes. In high pressure 
boilers, this tube cannot be applied in its simple form, as it 
would become of inconvenient length. 

We have, however, seen more than one ingenious modifica- 
tion of this apparatus, in which the communication with the 
steam is effected by a valve that is intended to open when the 
water falls below its proper level, and to close after the supply 
has been introduced. 

If a substance of convenient form, denser than water be 
taken, and be made to communicate with a lever on the outside 
of the boiler, by means of a wire passing through a stuffing box, 
it may be made just to float at the surface of the water by a 
counterpoising weight suspended from the opposite end of the 
lever. When the water falls, the floating substance will pre- 
ponderate, and the lever will incline towards it ; when the 
water is too high, the inclination will be in the opposite direc- 
tion ; and these deviations of the lever from the horizontal 
position, may be marked by an index at right angles to it, and 
affixed to its centre of motion. 

In stationary engines, particularly those employed in manu- 
facturing establishments, this method of indicating the position 
of water in the boiler has been successfully employed ; but in 
steam-boats its use may not only lead to uncertainty, but be 
actually productive of danger. In the motion to which 
boilers are often subjected in the latter case, the water is con- 
tinually shifting, and the whole boiler is sometimes filled with 



BOILERS. 67 

a foam composed of an intimate mixture of water and steam. 
The same remark applies to the case of locomotive engines, 
and it is by no means certain that any floating apparatus will 
act when the water foams. 

45. The boiler may be supplied as often as appears necessary 
from the indications of either of these apparatus, by different 
means, that must vary according to the elastic force of the ge- 
nerated steam. If the steam have a force but little greater than 
an atmosphere, a simple tube, having a top shaped like a fun- 
nel, will answer the purpose. This .must be inserted into the 
boiler through a steam-tight joint, until it nearly reaches the 
bottom, and it must be high enough to contain a column of wa- 
ter equivalent to the excess of the power of steam over the 
atmospheric pressure. The steam being of a constant elasticity, 
the water will stand in this tube at a constant height above the 
level of the water in the boiler, and if water be poured into 
it, an equal quantity must pass into the boiler. To adapt this 
to high pressure engines, a tube of inconvenient length would 
be necessary ; recourse must therefore be had to other means. 

The most simple of these is a spherical vessel, connected 
with the boiler from beneath by a tube and stop-cock, and 
closed at top by another stop-cock, surmounted by a funnel. 
The stop-cock is at first closed, and the sphere filled through 
the funnel and upper stop-cock ; the upper stop-cock is then 
shut : and, when it is known that the boiler needs a supply, the 
lower stop-cock is opened, through which the water will now 
pass to the boiler. The alternate action of these stop-cocks, in 
the first instance, prevents the steam from escaping, and from 
interfering with the entrance of the water ; and, in the second, 
permits the water to enter the boiler, while it is replaced by 
the entrance of steam into the spherical vessel. See PI. IT., 
Fig. 2. This apparatus is no longer applied to its original pur- 
pose, but under the name of a globe-cock is employed to intro- 
duce grease into the parts of high pressure engines. 

The operation of such an apparatus may be facilitated by 
making two parallel passages through each of the cocks. 
One of these is in each made, when the stop-cock is open, to 



68 BOILERS. 

adapt itself to a tube, which reaches from each stop- cock 
nearly to the opposite side of the spherical vessel. When the 
upper stop-cock is opened, the water will enter through the 
tube, and the enclosed air or steam will escape at the other 
passage of the cock. When the lower stop-cock is open- 
ed, the water will rush through the naked opening, and steam 
rise to replace it through the tube. 

A forcing pump may also be used to supply high pressure 
boilers, the pressure on the piston of which must be greater than 
the elastic force of the steam. A valve, by which the water 
the pump propels, may be made either to enter the boiler, or 
run to waste, at pleasure, will then supply the water that may 
be needed. This is the mode which is now universally used in 
all boilers which generate steam of a tension of more than one 
and a half atmospheres. See PL IV., Fig. 6. 

In all cases, however, it would be better, if possible, that the 
feeding apparatus should be self-acting ; or, to speak more pro- 
perly, that it should be governed in its operation by the level at 
which the water stands in the boiler. 

For boilers which generate steam not exceeding l£ atmos- 
pheres, the construction of such an apparatus is attended with 
but little difficulty ; but as methods of applying it safely at 
higher tensions are now coming into almost general use, what 
we are about to say on this subject is fast becoming a matter 
of history, rather than one of practical utility. We shall 
therefore describe them for the purpose of exhibiting the inge- 
nuity by which this part of the low pressure boiler was made 
to conform to the action of the engine, and not as applicable in 
the present state of our knowledge of the best mode of using 
steam. 

The most obvious and simple of all, and it is equally applica- 
ble to high and low pressure boilers, is a ball floating on the 
surface of the water, and attached by an arm to a stop-cock 
upon the supply pipe. This stop-cock is opened when the 
ball falls, and shuts when it rises. It may be attached in a 
low pressure boiler to a pipe, of a length sufficient to bear a 
column of water equivalent to the excess of the force of the 



BOILERS. 69 

steam above an atmosphere ; but in a high pressure engine it 
must be adapted to the pipe proceeding from a forcing pump. 

This method is liable to the objection of being subject to get 
out of order, and of being out of sight and reach ; it may, 
therefore, fail at the moment it is least expected. 

The floating ball may be made to act, through the interven- 
tion of a lever and a rod, upon a conical valve in the feed-pipe. 

A floating apparatus, similar to that which has already been 
mentioned for indicating the level of water in the boiler, may 
be made to regulate the supply of a low-pressure boiler. In the 
first place, the lever there described may have its centre of mo- 
tion in the axis of a stop-cock to which it is attached. In the 
second place, a conical valve may be attached, by a rod, to the 
arm of the lever that carries the weight. Around this rod is a 
small reservoir of water, communicating with the boiler be- 
neath by a pipe reaching nearly to the bottom. The conical 
valve is adapted to the junction of this pipe with the reservoir 
in such a manner as to open the communication when the float 
falls, and close it when the float rises. >See PL II., Fig. 8. 

For reasons which have already been mentioned, this method 
is not applicable to the boilers of steam-boat and locomotive en- 
gines. 

In most cases engines do not require to be kept in constant 
action. Those employed in manufactories are always stopped 
at night, and generally while the workmen are at their meals. 
As the action must be kept up until the end of the working 
hours, a great loss of heat is caused by the sudden cessation of 
the motion of the engine at a moment when the steam has its 
full tension. This loss has been in a great degree prevented 
by a modification of this feeding apparatus invented by Hall of 
Glasgow. In this modification the float is double, one part lying 
at the level at which the steam is to be maintained while the 
engine is at work ; the other within a few inches of the top of 
the boiler. The counterpoise is made up of two weights. 
These, when united, counterpoise the floats when the lower one 
is at the surface of the water in the boiler. On removing one 
of the weights, that which remains becomes a counterpoise to 
the double float when its upper part reaches the surface of the 



70 BOILERS. 

water. The water will, therefore, flow from the cistern of the 
feeding apparatus until the lower re-assumes its horizontal po- 
sition. On the replacing this weight, the engine will work off 
the water which has been thus introduced before the feeding 
apparatus will begin to admit water. 

By this arrangement, water is introduced at the temperature 
of condensation as soon as the engine is stopped, and the fire 
will be employed in bringing up to its working temperature 
during the interval of work. In the application of it to the en- 
gine of the Glasgow Water Works, a saving of nearly twenty- 
five per cent in the fuel consumed was obtained. The same me- 
thod is, of course, applicable to ferries, and to passage boats 
which have occasion to stop at landings ; and there would be 
no difficulty in graduating the water thus admitted to the in- 
tervals in the working of the engine. 

In the great change which is taking place in the manner of 
working condensing engines by which high steam is advan- 
tageously employed, all these modes so ingeniously planned to 
regulate the supply of boilers, may be said to have become in a 
great degree obsolete. In particular, it may be questioned 
whether any apparatus governed by a float will be sure to work 
in a steam- boat, a locomotive, or even a fixed high pressure en- 
gine. 

The supply of high pressure boilers, as has already been sta- 
ted, is always effected by means of a forcing pump. See PL 
IV., Fig. 6. 

This propels, by the action of the piston a b, a stream of wa- 
ter into a pipe furnished with two stop-cocks or valves, c and d, 
that act alternately ; by one of these, c, water is admitted into 
the boiler, by the other, d, it is allowed to run to waste. These 
valves are usually left to the care of the engineer, as an appa- 
ratus to render them self-acting is necessarily complex. We, 
however, give a drawing of one, the invention of a Mr. Frank- 
lin, that has received the medal of the British Society of Arts. 
See PL II., Fig. 1. 

All feeding apparatus should be sufficient to supply the boil- 
er with considerably more water than it usually evaporates. 
Generally speaking, it is made to furnish five or six times as 



BOILERS. 71 

much, as it is far better that water should run to waste, than 
that there should be at any time a want of a full supply. 

It will be obvious, that a self-acting feeding apparatus that 
will perform its duty when the engine is at rest, is still a de- 
sideratum for high pressure boilers. It is in the case of steam 
boats and locomotive engines that such an apparatus is almost 
indispensable, in order to place them wholly beyond the reach 
of danger, and to the want of it many fatal explosions are to be 
attributed. Many propositions have been recently made to sup- 
ply this desideratum, but none have come into general use. In 
the absence of a self-acting apparatus, force pumps, to be work- 
ed by hand, are applied to the boilers of steam boats and to locomo- 
tive engines. They also serve to fill the boiler in the first in- 
stance. 

46. A regular supply of water is not only necessary to keep 
up the flow of steam, but is of great importance to the safety of 
a boiler ; we have therefore treated of it next in order to the 
material. 

Whatever precautions may be taken in the choice and adjust- 
ment of the strength of the material, and, in giving a regular 
supply of water, it is indispensable, before a boiler is made use of, 
that it should be proved. This is necessary, because the proof 
shows defects that would otherwise escape notice, particularly 
at the joints of the wrought metals, while in cast iron there 
are frequently cavities that are not seen upon the surface. 
These different defects might cause a boiler to burst with 
violence if it were to be subjected to the action of steam before 
proof had been performed in some other manner. This pre- 
liminary proof is best effected by means of the hydraulic press, 
or water pressure pump of Bramah, whose principle has been 
explained on page 9. This method is, however, still defec- 
tive, inasmuch as it must be performed, if not with cold water, 
with that which is far below the heat to which parts of the boil- 
er must be afterwards subjected. 

It has been proposed to apply a pressure five or six times as 
great as the boiler is intended to bear. Nor is this too great a 
precaution, for the water proof is performed when cold, and we 



72 BOILERS. 

have seen that some metals are more tenacious when cold than 
when heated, and the proportion of six to one, at least, is neces- 
sary before this difference is obviated. If a boiler be not sub- 
jected to such a proof, it may be possible that when heated its 
limit of rupture may be reached before the safety valve opens. 

The water proof having been performed, the boiler should 
next be subjected to a similar trial by steam, say of four or five 
atmospheres more than is usually to be generated in the boiler 
without causing its safety valves to act. In France, it is re- 
quired by law, that all high pressure boilers be subjected to a 
proof five times as great as the boiler is intended to bear when in 
service. It is, however, to be considered that, when the boiler 
is to be used to generate high steam, such excessive strain would 
rather tend to increase the danger than to ensure safety ; for if 
the strain to which the metal is exposed exceed the limit of its 
elasticity, is will be materially weakened, although it may not 
explode under the proof. 

47. The next precaution to be taken is, that the boiler be 
furnished with safety valves. A safety valve is a conical or 
cylindrical stopper inserted into, or resting upon a seat of the 
same shape, and kept in its place by a weight equal to the 
most intense pressure that is intended to be exerted upon it by 
the vapour from within the boiler. When the steam acquires 
a force greater than this, the safety valve will open and permit 
the steam to escape ; at all inferior temperatures it will remain 
shut. Three things must therefore be investigated in order to 
their preparation, viz : the size of the opening to which they 
are to be adapted, the load they are to bear, and the proper 
mode of placing them. 

The openings must be large enough to permit all the vapour 
that can be formed to escape. This may be estimated at the 
conversion into steam of a cubic foot per hour from every- eight 
or ten feet of fire and flue surface. But as the safety-valve will 
probably be most needed when the fire has been augmented 
beyond its proper quantity, it will be well to prepare for the 
escape of, at least, four times that quantity, say a cubic foot of 
water evaporated for every two feet of fire surface ; this is the 



BOILERS. 73 

maximum of steam that can be formed under any ordinary cir- 
cumstance. 

The vapour will escape with a velocity that will depend 
upon its elastic force, but which increases much less rapidly 
than that does. We subjoin the velocities under different ex- 
pansive forces. 

Table of the Velocity of steam at different temperatures. 



r 

Expansive 


force. 

Atmospheres, 
do. 


- 


- 


- 


Velocity per second. 

- 873 

- 1145 




lf 




do. 


- 


- 


- 


- 


1296 




2 




do. 


- - 


, 


- 


- 


1405 




3 




do. 


- 


. 


- 


- 


1548 




4 




do. 


. 


. 


. 


- 


1663 




5 




do. 


- 


. 


- 


. 


1725 




6 




do. 


. 


. 


. 


. 


1785 




8 




do. 


. 


- 


- 


. 


1852 




10 




do. 


- 


. 


- 


. 


1993 




12 




do. 


- 


- 


. 


. 


2029 




14 
16 




do. 


. 


. 


. 


.~ 


2052 






do. 


. 


. 


. 


. 


2072 




1 IS 

20 




do. 


. 


. 


. 


. 


2084 






do. 


. 


. 


. 


. 


2098 




IL 














. . j 





The quantity obtained, by multiplying these velocities by the 
area of the opening to which the valve is adapted, must be 
diminished by the constant fraction that represents the section 
of the vena contracta in fluids ; this, in such an orifice, is about 
fths or .75. 

To determine the quantity then, that will issue by a given 
safety valve, three-fourths of its area must be multiplied by the 
velocity under the anticipated expansive force. When the 
quantity to be discharged per second is given, the reverse of 
the operation will give the proper area of the safety valve. 
The bulk of steam generated by the evaporation of any given 
quantity of water, may be found by multiplying the bulk of 
the water by the number representing the volume of steam of 
that temperature, on page 21. 

It will not be attended with any inconvenience to make the 

10 ' 



74 BOILERS. 

safety valves of high pressure boilers as large as those used for 
steam of less elasticity, and this is the method which is adopted 
in practice. 

The weight, with which the upper surface of a safety valve 
is to be loaded, should be equal to the pressure which the va- 
pour, at the maximum temperature for which the boiler is cal- 
culated, is capable of exerting upon the lower side of the safety 
valve. When this expansive force of the steam, at the given 
temperature, is estimated in atmospheres, one atmosphere, or 
151bs. per square inch, is to be deducted from the estimate, in- 
asmuch as the escape of the steam is opposed by the pressure of 
the atmosphere itself, which therefore acts as a part of the 
weight with which the safety valve is loaded. Therefore, to 
find the weight : 

The area of the safety valve in square inches must be mul- 
tiplied by 15 times the number of atmospheres to which the 
expansive force of steam at the given temperature is equiva- 
lent, less one : the product is the weight in pounds. 

The weight in most cases acts upon a lever of the second 
kind, by the intervention of which the pressure is increased. 
As the foregoing rule gives the pressure that ought to act upon 
the safety valve, the weight that is suspended from the lever 
must be diminished, in the ratio by which the whole length of 
the lever exceeds the distance between the fulcrum of the lever 
and the safety valve. 

The number of atmospheres, to which the expansive force of 
steam, at different temperatures, is equal, may be found by the 
table upon page 23. 

There is a curious phenomenon which occurs when steam 
issues from a safety valve, or other orifice ; the temperature 
of the vapour just without the opening, is lower, the higher the 
tension of the steam is within the boiler. Thus steam issuing 
from a boiler, the water within which is at 212°, scalds the 
hand ; while if it had a tension of several atmospheres, the heat 
would be easily borne without injury. This phenomenon, 
which at first sight appears almost paradoxical, grows out of the 
rapid dilatation of dense steam, and the consequent increase of 
its capacity for specific heat. The greater the tension, and 



BOILERS. 75 

consequent density of the steam, the greater will be the diminu- 
tion of temperature. 

This explanation would teach us that the size of safety- 
valves, as calculated from the table on p. 24, is less than they 
ought to be in practice, and no inconvenience can arise from 
making them of such size as will allow the escape of low steam ; 
for the weight will close the valve as soon as the tension of the 
steam is sufficiently diminished. 

Safety valves, generally speaking, are of the figure of a frus- 
tum of a solid cone, ground to fit a hollow frustum of an equal 
hollow cone. They may, as has been stated, be pressed down 
by a weight, acting directly, or through the intervention of a 
lever. In the former case the weight may either hang from 
the valve within the cylinder, or be fastened to its exterior 
surface. A valve of this description furnishes a constant pres- 
sure, and ought to be adapted to the highest temperature the 
boiler is intended to bear. If it act by means of a lever, the 
pressure of the weight, when at the extremity of the lever, 
ought to be equal in its action to the same maximum tension ; 
but, by making it act nearer to the fulcrum, its action may be 
made equivalent to the expansive force of steam of lower tempe- 
ratures. The latter is, therefore, best adapted to the case 
where the action of the boiler is left to the discretion of the fire- 
man ; while those where the weight acts directly, may be en- 
closed and kept beyond his reach. 

On Plate I. are to be seen several varieties of the safety 
valve. Fig. 1 0, is a conical valve, whose weight is suspended 
beneath it, and hangs within the boiler. Fig. 11, is one, also 
conical, whose weight lies above it, and without the boiler. 
Fig. 1*2, is another of the same shape, and bearing a weight 
upon it, which is enclosed in a cylinder in such a way that it 
may be shut up beyond the reach of the workmen. Fig. 13, is 
a cylindrical safety valve, working in a pipe and pressed down 
by a spring ; when the pressure of the steam overcomes the 
elasticity of the spring, the lateral openings in the pipe are un- 
covered in succession, and the space for the escape of steam in- 
creases with its tension. A safety valve, pressed down by a 
lever bearing a weight, is represented upon PI. II. at Fig. 7. 



76 BOILERS. 

The best mode of regulating the length of the arms of the 
lever to each other, is to make them in the ratio which the sur- 
face of the valve bears to the unit of superficial measure. Thus, 
if the surface of the valve be five square inches, the arms of the 
lever should be in the ratio of 5 : 1. The advantage of this 
method is, that the weight which is applied to the lever is the 
exact measure of the pressure on each square inch of the valve. 

In locomotive engines, a suspended weight is liable to an os- 
cillating motion, which varies its pressure upon the valve, and 
may cause it to be continually opening and shutting. For this 
reason, instead of a weight, a spring has been substituted. 
This, being made upon the principle of the common spring 
weighing machine, may give any required pressure on the lever 
of the safety valve beneath a given limit. The tension of the 
spring is adjusted by means of a screw, which draws out the 
spring until its index marks upon a scale the weight for which 
the tension is intended to be a substitute. 

In all boilers there ought always to be two valves, one of 
which is left to the care of the fireman or engineer, the other 
fitted to the intended maximum pressure of the contained steam, 
and closed up. Very serious accidents have frequently occur- 
red from leaving safety valves wholly to the control of a work- 
man, or even of the captains of steam vessels, who may feel a 
temptation to increase the pressure of steam beyond what the 
boiler is capable of bearing. The proper situation of the safe- 
ty valve is upon the top of the boiler: and when there are two, 
one should be at each end ; that left to the discretion of the 
workmen at the end next the fire, so as to be within their reach ; 
that which is beyond their control, at the farther extremity. 
When the aperture by which the boiler is entered for the pur- 
pose of cleansing it, is situated on the top, the safety valve is 
often placed in its cover. 

In consequence of a remarkable fact that has recently been 
observed, much doubt has existed as to the certainty of the 
action of a safety valve. When air is strongly compressed in 
a vessel or pipe, and issues thence by an orifice in a plane sur- 
face, if a plate or disk be presented to the orifice by one of its 
plane surfaces, so far from being driven away, it will be retain^- 



BOILERS. 77 

ed at a very small distance from the orifice. In this case the 
air escapes in the form of the surface of a very obtuse angled 
cone around the edges of the disk, leaving a conical vacuum 
beneath ; and in consequence of the well-known fact that there 
is a lateral communication of motion from a current of fluid to 
neighbouring portions of the same or other fluids, the air above 
the plate moves towards it in order to join the stream ; the 
vacuum beneath, and current from above, united, retain the 
disk at a constant, but small distance, from the plane in which 
the orifice is pierced. It has been found that the escape of 
steam is attended with similar phenomena. Still, however, in 
conical safety valves, if thin, there is no reason to apprehend 
any danger from this source. In those of the usual form, the 
increased resistance growing out of this cause, will not exceed 
one-twentieth of an atmosphere, or three-fourths of a pound 
upon each square inch. But were the valve to have the form 
of a frustum of a cone, whose height is great in proportion to 
the aperture, the resistance might become enormous ; and, in 
the case of some experiments that were made in reference to 
this subject, it amounted to upwards of thirty atmospheres. 
Here, then, we have a strong reason in confirmation of the pro- 
priety of the usual practice of making the safety valves of high 
pressure boilers of the size of those of condensing engines. 

However carefully a safety valve may have been construct- 
ed, it may, notwithstanding, cease to act, in consequence of rust, 
which will fix it to its seat. This is much more likely to hap- 
pen when it has been long shut, but may occur even to valves 
in frequent action. Still, however, to open the valve from 
time to time is the best preventative ; for a safety valve that 
has remained closed for a week, no longer deserves the name. 

Large boilers of but little strength, as employed for genera- 
ting low steam, are sometimes exposed to a danger of an oppo- 
site nature. When the fire is extinguished, the steam within 
will be condensed and a partial vacuum formed, the external at- 
mosphere will now act, and may cause the boiler to collapse. 
It has been proposed to remedy this defect by an air valve. 
A conical valve opening inwards, and kept in its place either by 
a counterpoise or a weak spring ; if either of these be little more 



78 BOILERS. 

powerful than the weight of the valve itself, they will keep it 
in its seat so long as the tension of the steam within exceeds 
that of the atmosphere ; but when the latter becomes the most 
powerful, the valve will open and admit air. 

We have stated, that when the space intended to be occupied 
by water becomes narrow, it may be wholly displaced by 
steam. In such case danger will arise from the burning of the 
metal, and from the heating of the steam after it is generated. 
To meet this danger, an ingenious person of the name of Doug- 
las has proposed to place in the bottom of boilers a valve 
opening inwards ; and he asserts that he has seen it in action even 
when the boiler contained steam of 4 or 5 atmospheres. We 
do not pretend to vouch for the fact, which appears contrary to 
mechanical laws ; but that it should be true, is not more extra- 
ordinary than many of the cases of violent explosion. 

49. Lest the safety valve or valves should by some accident 
become fixed to their seat, it is important that there should be 
some means of determining, at any moment, the elastic force of 
the steam within the boiler. Apparatus for this purpose are called 
Steam Guages. The simplest form of these is a bent tube, the 
two branches of which are parallel; one of these branches is 
open to the air, the other is bent in such a manner as to be 
adapted to an opening in a part of the boiler above the level of 
the water it contains, or to the steam pipe, and is soldered or 
sealed to it in such a manner that steam cannot escape by 
the joint ; this tube, if empty, would permit steam to escape 
through it, but mercury is poured in to fill the bend, and rise 
some inches in each branch of the tube. When the expansive 
force of the contained steam is just equal to an atmosphere, the 
mercury will stand at equal heights in each branch of the tube ; 
when the pressure increases, the level of the mercury, in the 
branch nearest the boiler, will be depressed, and that in the 
open branch raised ; the sum of the two equal changes of level 
will be the measure, in inches of mercury, of the expansive 
force. As the changes of level in the two branches are equal, 
it is sufficient to measure that of the outer tube alone ; this is 
done by a scale on the side, if the tube be of glass : but if of iron, 



BOILERS. 79 

by placing in it an iron rod, which floats upon the mercury ; and 
which just reaches the top of the tube when the two columns 
of that fluid are of equal height. The tube or rod might be 
graduated by division into half inches, each of which would 
correspond to a difference in the two levels of a whole inch, 
the thirtieth part of an atmosphere, or half a pound upon each 
square inch of surface, over and above one atmosphere. 
Were the guage to be graduated to inches, each inch would 
correspond to one pound of internal pressure against the 
weight with which the safety valve is loaded ; and this is the 
mode of graduation most usually employed in this country. 
A guage of this form is represented on PL I., Fig. 7. By add- 
ing: to the length of both branches of the tube, making; it of a 
strong material, and increasing the quantity of mercury, this 
guage may be fitted for steam of any elastic force, but it might 
in that case become inconvenient to observe its indication by 
means of a graduated rod. In such cases a float of iron may 
rest on the surface of the mercury in the open branch, and be 
attached, by a cord passing over a pulley, to a counterpoise ; 
the ascent and descent of which, along a graduated scale, 
would mark the difference of level upon the same principle as 
the rod. 

A straight tube, inserted nearly to the bottom of a close cistern, 
which communicates at top with the steam of the boiler, and 
which contains a mass of mercury, will also answer this pur- 
pose. If the surface of the cistern be large in proportion to 
to the area of the tube, the change of level within it may be 
neglected, and the height of the mercury in the tube measured 
in inches. See Plate I., Fig. 8. 

The steam guage may be made to act as an additional safety 
valve. In this case its height must not exceed that which will 
measure, in a column of mercury, the maximum pressure the 
boiler is intended to bear ; and the top must be widened into the 
form of a funnel, sufficiently large to contain all the mercury 
with which the tube is supplied. Such an apparatus, with the 
arrangement of float and counterpoise sliding in a scale, is re- 
presented PI. I., Fig. 8. 

A guage for a high pressure boiler may be made by immers- 



80 BOILERS. 

ing the lower end of a glass tube in a basin of mercury ; the 
upper end of the tube is closed, and it contains atmospheric air. 
The basin of mercury is enclosed in a case communicating with 
the boiler. The steam, acting on the surface of the mercury, 
will force it up the tube and compress the air, and the space that 
it occupies, being according to the law stated on p. 14, inverse- 
ly as the pressure, will show the tension of the steam. Such a 
guage is represented at Fig. 8, on PL I. 

50. Should the fire be more intense than is consistent with a 
regular supply of steam of the required temperature and pres- 
sure, an apparatus has been contrived to moderate its action, 
by the very increase in elastic force which it communicates to 
the steam. This is called the self-acting or self-regulating 
damper. Hitherto they have only been applied to boilers con- 
taining steam of so small an elasticity as to be capable of being 
supplied with water by an open feed-pipe, as described § 45. 

The water stands in this pipe at a height above that in the 
boiler, which depends on the difference between the elastic 
force of the steam and the pressure of the atmosphere. A 
plate of iron, sliding in a vertical groove at the throat of the chim- 
ney, is attached to a float resting on the surface of the water in 
the feed-pipe by a cord passing over pullies ; when the float rises 
by an increased action of the steam, raising the water in the 
feed-pipe, the damper will descend, and when the float descends, 
the damper will be raised. It will, in the former case, lessen, 
and in the latter, increase the aperture of the chimney, and the 
draught will vary with the size of the aperture, as has already 
been stated. Such an apparatus is represented as attached to 
the boiler, Fig. 1, PI. I. n is the float, o the pully. The use 
of a self-acting damper is liable to the same difficulties as that 
of a self-acting feeding apparatus. It is hence scarcely or ne- 
ver used, except the steam is of very moderate tension. 

51. In addition to a self-regulating damper, there should be 
another, to be worked by hand as occasion may require ; and 
in order to place the fuel completely under the control of the 
fireman, the passage by which air is admitted to the ashpit 
ought also to be capable of being opened and shut at pleasure. 



BOILERS. 81 

Doors and valves for this purpose should therefore be provided, 
and the apparatus is called a Register. Such dampers are 
placed in the chimneys of almost all our steam-boats, and tem- 
porary doors to the ashpit are made of plates of sheet iron. 

52. There are dangers, however, to which boilers are expos- 
ed, against which safety valves and self-acting dampers present 
no security, and of which steam guages give no notice. As a 
general rule, it is no doubt true that the temperature and ten- 
sion of vapour bear a constant relation to each other ; but it 
may so happen that steam, after being generated, is raised to a 
high temperature without exerting a proportionate expansive 
force. Thus, if a portion of a boiler should acquire a heat great- 
er than the water contained in the other parts, as it may do 
when not covered with water, the steam will receive an excess 
of heat without acquiring a proportionate elasticity. In ex- 
periments made by Mr. Perkins, steam was heated to a tem- 
perature at which, if of a corresponding density, it ought to have 
exerted a force of 56000 lbs. per square inch, but which did 
not exert a pressure of more than 150 lbs. The reason is ob- 
vious, for it was enclosed in a separate vessel, and its quantity 
remaining constant, it did not increase in density. Had, how- 
ever, a small additional quantity of water, heated under pres- 
sure to a high temperature, been injected, it might be inferred, 
that the steam would have acquired the density necessary to 
enable it to exert the force corresponding to its temperature. 
Perkins also established the truth of this inference by actual 
experiment. Water was heated in one of his generators, the 
safety valve of which was loaded with a weight of 60 atmos- 
pheres, to a temperature of upwards of 900° ; a receiver was 
prepared, void of both air and steam, and heated to upwards of 
1800° ; a small quantity of water was then made to pass from 
the generator to the receiver ; this was instantly converted into 
steam, whose heat was sufficient to inflame the hemp that 
coated the tube, at a distance of 10 feet from the generator ; its 
temperature was therefore estimated at not less than 1400°. In 
spite of this high temperature at which the steam was formed, 
its pressure did not exceed five atmospheres. But by injecting 

11 



82 BOILERS. 

more water, although the temperature was lessened, the elastic 
force was gradually increased to 100 atmospheres. In phe- 
nomena of this description we may find the cause of many 
explosions that cannot be explained on any other principle. 

If we suppose that the supply of water is impeded, neglect- 
ed, or checked altogether, the level of that in the boiler must 
descend, and parts exposed to the action of the fire may become 
dry ; such parts may then be heated far beyond the tempera- 
ture of the water beneath ; and the vapour may be rendered by 
them sufficiently hot to make other parts of the boiler lumi- 
nous. If, by any cause, the water from beneath be brought in- 
to contact with the vapour and heated surfaces of the boiler, it 
will be instantly converted into steam of great expansive force, 
and in quantities for which the usual safety valves are not suf- 
ficient to provide an escape. An explosion must therefore 
ensue. 

The water may be brought into contact with these heated 
parts of the boiler, or with the hot vapour, by the very means 
that in other cases would be applied to diminish the danger. 
Thus, if the safety or throttle valve should be opened, the wa- 
ter, which was before boiling quietly, will suddenly rise with 
violent ebullition, or if the feeding apparatus begin again to 
act, the level of the water will be raised. In both cases, a con- 
tact will take place with the red hot surfaces, and with the in- 
tensely heated steam. 

There are also other cases in which the space usually occupied 
by water, and even the whole boiler, becomes filled with a foam- 
ing mixture of steam and water. The circumstances are similar 
to those of a pot boiling over. In such cases the metal of the boil- 
er and flues may be heated to incandescence, for such a mixture 
is a bad conductor of heat. Here again the injection of water 
into the boiler, or the opening of the valves, may be attended 
with danger. 

Water also, as has been stated (§16,) if heated to 680°, tends 
to assume the gaseous form, and then exerts a pressure which no 
vessel, constructed as boilers usually are, is capable of resisting. 
It is also within the limit of possibility that in iron boilers an 
explosive mixture may be generated. The metal, when red hot, 



r 



BOILERS. 83 

will decompose the steam, and hydrogen will be liberated. If by 
any means oxygen can be introduced, the same heat will cause 
it to explode ; but oxygen cannot enter until the tension within 
the boilers become less than an atmosphere. 

These have been admitted to be the only causes of the explo- 
sion of boilers, whether of low or high pressure. When boilers 
give way under the force of steam alone, dangerous consequen- 
ces appear to have rarely happened. We have ourselves been 
twice in steam-boats, working with steam of not less than an at- 
mosphere and a half, when the boiler has given way ; and in 
neither case was the accident known to the passengers, except 
by stopping of the machinery. 

The wrought iron boiler of a high pressure engine, working 
with steam of the tension of six atmospheres, gave way some 
years since in a manufacturing establishment in the city of 
New- York, and the only bad effect was the extinction of the fire 
by the efflux of water. 

At Paris, the lower part of a boiler of cast iron, working with 
steam of the same force, gave way, and no other bad consequen- 
ces followed. 

In nearly all the cases where fatal accidents have occurred, 
the explosion appears to have been due to other causes than 
the mere expansive force of the steam that would be formed when 
the boiler is in proper order and supplied with water. There 
are, however, a few instances where the escape of large quantities 
of steam into close cabins, or its partial decomposition in pass- 
ing through the fire, have produced, suffocation. Neither can 
it be doubted that a boiler of equal or nearly equal strength 
throughout may give way with explosion under the action of 
steam gradually and steadily increasing in temperature. 

In the fatal accidents of the Chief Justice Marshall and Helen 
McGregor, the explosions took place after delay at stopping 
places, and followed almost instantly the opening of the throttle 
valve to set the engine again in motion. In the former, where 
the main internal flue gave way, the safety valve was either 
open, or had just been closed ; one of the persons on board re- 
marked a peculiar shrillness in the sound of the escaping steam, 
that can only be ascribed to its being intensely heated, without 



84 BOILERS. 

having a corresponding density ; another observed that it had 
a violet hue, which may perhaps be explained by supposing it 
to have been heated until it would have been luminous by night. 
In opposition to the opinion that the water had fallen too low 
and left the flues bare, it was stated by the captain that the 
guage cocks had been tried, but on examining the boiler it was 
found that they were situated on the side of the boiler nearest 
the landing ; and it is well-known that on such occasions the 
influx of passengers to that side is often so great as to change 
the level of the boat so much as to render the guage cocks, when 
so situated, useless. 

It is also possible that the fireman, who was by no means skil- 
ful, may have mistaken water of condensation in the tube for 
that coming from the boiler. This last mistake is one that 
ought to be carefully guarded against, by leaving the cock open 
several seconds. 

Of the intense heat that steam sometimes attains, even with- 
out causing explosion, the following instance may be cited : 
the packing of the piston of a steam-boat, working with steam 
of a tension no greater than an atmosphere and a half, burst 
into flame on opening the cylinder at least half an hour after 
the fire had been extinguished. Here it is evident that any 
mixture of heated water with this steam might have caused ex- 
plosion. 

Even the injection of water into an empty space, whose tem- 
perature is not below 680°, may cause explosion, by its being 
wholly and suddenly converted into steam of great density and 
expansive force. • 

The committee of the Franklin Institute have, in their report 
of a series of interesting and valuable experiments made by 
them, thrown some doubt upon the explanation given by Per- 
kins of the cause of the explosion of boilers. We do not, how- 
ever, consider their experiments as absolute proofs of the in- 
accuracy of his positions. We may remark, that in their expe- 
riments the density of the steam was never increased even to 
an approximation to what would have been consistent with the 
saturation of the space at its final temperature. Thus, in one 
of their experiments, the tension of the steam obtained by the 



BOILERS. 85 

injection of water upon the heated sides of a vessel was 12 at- 
mospheres, while the temperature was that of steam which, if 
saturated, would have exerted a force of 27^ atmospheres. Cold 
water was also used and injected, while in practice the water, 
which would be most likely to be mixed with steam heated af- 
ter it had been generated, would be that rising in foam from the 
lower part of the same boiler. 

If the committee of the Franklin Institute have left us in 
doubt as to the accuracy of Perkins' explanation, they have 
raised none as to the certainty of danger when portions of the 
metal of boilers become intensely heated. In addition to the 
causes assigned by him, they have shown that the tenacity of 
copper decreases as it is heated, even from low temperatures ; and 
that, although that of iron increases with the temperature up to 
alimit which is above that at which steam is usually employed, 
it decreases rapidly at temperatures above that limit, and at a 
red heat is no more than one-sixth of what it is when cold. 

Boilers, when the fire is made within, or when the return 
flues pass through them, are obviously far more subject to acci- 
dents arising from this cause than those heated from without ; 
low pressure boilers are as liable to them as high ; and it is con- 
fidently believed that very many explosions are to be attributed 
to this cause, against which the usual safety apparatus furnish- 
es no protection. To pay the greatest attention to keeping the 
feeding apparatus in order, and to have the means of ascertain- 
ing at every moment the height of the water in the boiler, are 
the surest means of defence; but as the first of these may fail, 
and does not act in many boilers after the engine is stopped ; 
and as the second depends upon the faithfulness of the engineer, 
or may also be clogged, and cease to give true indications ; 
other means have been proposed. 

53. The first of these is a thermometer, inserted through a 
collar into the part of the boiler occupied by the steam, and 
which will therefore indicate its temperature. It must be made 
to mark the higher temperatures only, and may be graduated 
by a standard instrument, in a bath of hot oil. This is, how- 



86 BOILERS. 

ever, but a fragile instrument, and may also be neglected by 
the workmen. 

54. Another method, which promises to be effectual in many 
cases, is to form a part of the boiler of a plate of metal fusible 
at a comparatively low temperature. Such is an alloy of bis- 
muth, lead, and tin, by varying the proportions of which a con- 
siderable difference in fusibility may be attained. They ought 
to be of such a mixture as not to melt until heated beyond the 
temperature assumed as the limit of the heat to which it is ever 
desired to raise the steam, but fusible at one considerably be- 
low that at which the boiler becomes red hot. From 20° to 
40° above the maximum heat the steam is meant to attain, will 
be well suited to the purpose ; for they will then melt before 
any part of the boiler can become red hot. These plates must 
be adapted to the upper part of the boiler, and be of course in 
contact with the steam ; they are inserted at the end of tubes 
fitted steam-tight to the boiler. As they are apt to soften long 
before they melt, they ought to be covered c by a diaphragm of 
wire gauze. When thus protected, they have been found not 
to give way until they actually melt. As different parts of the 
boiler may acquire different temperatures, two such plates will 
be needed upon its outer surface, at the two ends ; they ought 
to be as near to the body of the boiler as possible. When flues 
pass through the boiler, we conceive that it would be a proper 
precaution to furnish them also with plates of this description, 
but in this case the metal might be less fusible, and lead unal- 
loyed would suffice. It has been objected to plates of fusible 
metal, that when they give way, the engine becomes useless ; 
and that in steam-boats in particular, danger may arise from the 
proposed means of safety. But this objection has been fully 
obviated by an invention of Professor Bache of the University 
of Pennsylvania. In this, the tube in which the fusible plate is 
inserted, is prolonged above it far enough to allow the ap- 
plication of a safety valve, which may therefore be adapted, 
and close the opening, until a new fusible plate can be pro- 
cured. It has, however, been found easy to protect the fusible 



BOILERS. 87 

plates from the heat within the boiler, and they are thus ren- 
dered nugatory. 

When fusible plates are not used, and when from a ther- 
mometer, or from other appearances, there is reason to appre- 
hend that the water has fallen too low in the boiler, and that 
the temperature of parts of it have been raised to a dangerous 
degree of heat, the only means of safety are, to check the 
draught of the chimney by the damper, to lessen or extinguish 
the fire as soon as possible, or even to procure rapid cooling 
by pouring water on the outer surface of the boiler. The 
safety valve may then be opened ; and, after the cooling is com- 
plete, the boiler filled up by a hand force pump. A damper 
kept open by the action of the engine,,- and closing the instant 
it stops, would have a good effect, and might be easily adapted 
to a centrifugal apparatus. 

55. It has been proposed, as a mode of securing safety in 
cases of great increases of temperature in the upper part of the 
boiler, to provide safety valves that would open at the limit of 
temperature beyond which danger might ensue. A safety 
valve of the usual form, but loaded with a great weight, and 
placed upon a tube containing a cylinder of metal, will answer 
this object : let the metallic cylinder be supported from be- 
neath, and of such a length that the dilatation by heat shall 
bring it in contact with the safety valve at the required tem- 
perature ; any further increase of temperature will open the 
safety valve, and permit the escape of steam ; its action is cer- 
tain, for the expansive force of the metals when heated, is capa- 
ble of overcoming the most powerful resistances : but it is 
rather to be used as an indicator of the necessity of moderating 
the fire, and putting the feeding apparatus in order, than as af- 
fording perfect security from explosion. 

It is difficult to point out methods that are of themselves en- 
tirely to be relied upon to prevent explosions. However per- 
fectly a boiler may be constructed or furnished with safety ap- 
paratus, it will still depend much upon the carefulness and in- 
telligence of the persons entrusted with its management. One 
thing, however, appears certain, although contrary to general 



88 BOILERS. 

belief, that as the most usual causes of explosion affect low pres- 
sure boilers equally with those which generate high steam, the 
latter are not more subject to accident than the former. There 
are precautions, however, which, if resorted to, may diminish 
the risk of such accidents in a very great degree ; so far, indeed, 
that without the greatest carelessness, they cannot occur. These 
may, perhaps, be recapitulated to advantage. 

1. Cylindrical boilers, without any return flue, either without 
or within, are safer than any others. 

2. Internal flues should be avoided wherever it is possible, and 
especially the chimney, or vertical flue, should never be permit- 
ted to pass through the boiler. But if internal flues must be 
used, and they cannot be avoided in steam boats and locomotive 
engines, the plan of diminishing them to mere tubes is the best, 
and care must be taken that the spaces between them are not 
too small. 

3. Every boiler should be furnished, in addition to the usual 
safety valve, with one not under the control of the fireman. 

4. All boilers should be furnished with guage cocks, or other 
apparatus, to show the level of the water, and these should be 
so placed in steam boats, that no error in their indication can 
take place when the vessel heels or rolls. 

5. Plates of fusible metal should be provided, of a composi- 
tion melting so far above the usual temperature of the water 
and vapour, that they will not open on any ordinary occasion, 
but will give way before they attain a temperature that can be 
dangerous ; and these should have the addition proposed by Pro- 
fessor Bache. 

6. A thermometer may be introduced into the boiler, whose in- 
dications may be seen from without. 

7. Self-acting feeding apparatus should be adapted to the 
boiler, by which water will enter, and keep the fluid within at 
a constant level ; and this should depend upon the waste of wa- 
ter, and not on the action of the engine. It unluckily happens 
that no such apparatus has yet been introduced into use which 
is adapted to high pressure engines, nor indeed for any where 
the tension of the steam exceeds 1 i atmospheres. Neither are 
they always applied even to low pressure engines ; and in those 



BOILERS, 89 

f 

intended for steam boats, they would be worse than useless, 
from the uncertainty of their action.' 

8. The chimney should be provided with a damper by which 
the draught of the flues may be suddenly checked, and doors 
should, if possible, be placed upon the ashpit. A damper that 
would close as soon as the engine ceased to move, would be of 
great service in lessening the liability to explosion, and this 
does not appear to be difficult of attainment. 

9. The proof of the boiler should be conducted with the 
greatest care, first with water, at a pressure five or six times as 
great as the boiler is intended to carry, and afterwards with 
steam of more than the highest possible tension. The water 
proof should be repeated from time to time, and every part care- 
fully examined to ascertain that all the safety apparatus is in 
working order. In high pressure boilers, the force pump with 
which they are fitted is well adapted for giving the water- 
proof. 

Few or none of these precautions are usual in our American 
steam boats : the boilers, even if cylinders, have both internal 
flues and furnaces, and the vertical chimney frequently rises 
in the boiler ; there is never more than one safety valve ; plates 
of fusible metal are unknown ; the feeding apparatus is merely 
a forcing pump, which is turned on or thrown off at the pleasure 
of the engineer, and which does not act at all at the time the 
engine is not in motion 5 but a very few steam boats have 
dampers upon their flues ; in fine, the proof is wholly a matter 
between the maker and proprietor, and for its proper performance 
the public have no guarantee. Thus, of all the precautions 
that have been proposed in order to insure indemnity from ex- 
plosion, but two are in use among our steam boats ; namely, the 
safety valve and the guage cocks ; the former being still sub- 
ject to the caprice of the persons employed, and the latter having 
an uncertainty in their indications, both when the boat inclines 
to either side, and when they contain, as they most frequently 
will do, water of condensation. They are also of no value when 
the water in the boiler foams. 

The means which are used are not certain to insure safety, 
even where the care of the officers of the vessel, and of the per- 

12 



90 BOILERS. 

sons employed about the engine, is unremitting, and directed by 
the utmost intelligence ; hence dangerous accidents occur with- 
out giving rise to blame, and thus diminish a proper feeling of res- 
ponsibility. On the other hand, were the list of precautions that 
we have given, to be completed by a self-acting feeding appara- 
tus, independent of the action of the engine,, for a high pressure 
boiler, we conceive that no accident could possibly happen 
where they are employed, except through carelessness, inatten- 
tion, or fool-hardiness. 

Should it appear that the feeding apparatus does not act to 
supply as much water as is evaporated, the damper should be 
closed, and the boiler might even be cooled by the gentle applica- 
tion of water from without ; but it will always be a sure source 
of danger to inject water in abundance, or even to open the 
safety valve suddenly, after the water has once fallen below its 
proper level, and before it is ascertained that neither the tem- 
perature of the steam within, or of the sides of the boiler, are 
such as to cause a sudden conversion of the water that comes 
into contact with them into steam. 

55. In connexion with this subject, we have to mention and 
condemn an addition which is often made to the boilers em- 
ployed in our American steam boats. In consequence of the 
space which can be allowed for the boiler being limited, it has 
been found that the flame often passes into the chimney, and 
even issues from its upper opening. As much heat would be 
thus lost, it has been attempted to apply it to the steam, 
in its passage from the boiler to the engine, by enclosing 
the chimney in a cylindrical case called a steam-chimnej'', 
through which the steam must pass. This method is, however, 
the least advantageous mode of applying heat, for the steam, 
seated out of contact with water, is not rendered more elastic 
than air would be under similar circumstances, and has its 
energy far less increased than if the same heat was applied to 
the water in the boiler. On the other hand, dangers similar to 
those of which we have just spoken, occur ; and if the risk of 
the heated steam being mixed with water is less than if it were in 
the boiler, another source of accident is to be found in the rapid 



BOILERS. 91 

oxidation of the iron of the chimney, thus heated in contact with 
steam. This part of the chimney will, therefore, require fre- 
quent repairs, and if they be omitted, may give way with vio- 
lent explosion. To this cause the explosion of the steam boat 
William Gibbons, in the spring of 1836, is to be ascribed. It 
may therefore be stated, that the necessity for the use of a steam 
chimney is a proof of bad calculation in the plan of the boiler, 
and that the heat which it is intended to save by this means, 
may be much better applied. 

56. There is another species of danger which arises from the 
deposit of solid substances. Almost every kind of water that 
is used for boilers, contains more or less earthy and saline mat- 
ter. The constant evaporation is replaced by new supplies of the 
same impure water, and the soluble portion or mechanical im- 
purity is consequently accumulating. The soluble parts be- 
come greater in quantity than the contained water can hold in 
solution, and these are deposited, along with those that are 
merely suspended. Crusts thus form on the lower part of the 
boiler, and the surface covered by them, being no longer in con- 
tact with the water, may be heated red hot, and may be corrod- 
ed in consequence of the property that some of these salts have, 
of being decomposed by the metals at a red heat. The boiler 
will become weak in these places, and be liable to burst. It 
hence becomes necessary to cleanse the boilers frequently ; for 
this purpose, as well as for examining the interior, an opening 
is made in the boiler, large enough to admit a man. This has 
a cover, which, when the boiler is in use, is fastened down by 
screw bolts and nuts, and is packed in such a manner as to be 
«team-tis:ht. This opening is called the Man-hole. 

These deposits become frequent and copious when sea-water 
is used, and it has be found necessary, in consequence, to 
cleanse the boilers of steam boats that navigate salt water at 
least once a week. So soon as the boiler has received succes- 
sive supplies of salt water, amounting together to nine times its 
own capacity, a crust of a double sulphate of line and soda 
will begin to collect. A farther evaporation will cause the de- 
posit of salt, and finally of the chloride of magnesia. 



92 BOILERS. 

When the water is fresh, and the deposit principally consists 
of sulphate of lime, as is the case with hard pump waters, vege- 
table feculae will suspend the impurities. To furnish this, 
potatoes may be thrown into the boiler, in the proportion of 
half the weight of bituminous coal that is consumed per 
hour. This quantity of that root once added, lurnishes starch 
enough to keep the earthy matter suspended by the water for 
a long space of time, and it has not been found necessary to 
cleanse boilers, when this addition is used, oftener than once a 
month. It is not known whether the same method will be ef- 
fectual in preventing the saline deposits of sea water. 

The necessity of cleansing and scraping boilers in which 
sea water is used, may be in a great degree prevented by 
blowing off a part of the water from time to time. This 
method is, however, attended with a great waste of heat and 
consequent consumption of fuel. We shall have occasion to 
cite an improvement in the engine, by which it is ensured that 
the boiler shall be fed with distilled water ; and by the adoption 
of this improvement, all the dangers and inconveniences of 
which we have spoken may be obviated. 

57. It merely remains that we should speak of the pipes by 
which the steam is conveyed from the boiler to the engine. 
The size of these will depend on the quantity of steam the 
boiler is intended to furnish, the resistance the pipe itself oppo- 
ses to the passage of the steam, and the loss of heat. 

Steam issues into a space containing atmospheric air with 
the velocities given in the table on p. 73. The velocities with 
which it rushes into a vacuum are as follows, viz. 



BOILERS. 93 

Table of the Velocities with which Steam flows into a Vacuum. 



Force of Steam. 

1 Atmosphere, 








Velocity per second. 

- 1908 


2 do. 


- 


- 


- 


- 


1977 


3 do. 


- 


- 


- 


. 


2006 


4 do. 


. 


- 


. 


. 


2022 


5 do. 


. 


- 


- 


- 


2038 


10 do. 


- 


- 


- 


- 


2098 


15 do. 


- 


- 


- 


- 


2121 


20 do. 


- 


- 


- 


- 


2141 


L 













It will be seen from this table, that the velocity of effluent 
steam increases very slowly with increase of temperature. This 
grows out of the fact that the density of vapour increases under 
ordinary circumstances nearly as fast as its elastic force. Did 
both follow the same law, the velocity would not increase at 
all ; but the weight of steam expended by a given orifice, in- 
creases rapidly, for the density of hot steam is much greater, 
and the weight that passes out is in the compound ratio of the 
density and the velocity. 

The table on page 73 gives the velocity for high pressure 
engines, for they, as we shall see hereafter, are resisted by the 
pressure of the atmosphere. The table just given contains the 
velocities for condensing engines. Both of these, however, require 
a correction for the friction, and the loss of motion by cooling ; 
but for these it is impossible to give any general rule. A me- 
thod that has been found to succeed in practice is, to make the 
orifice, or nozzle, by which the pipe communicates with the em 
gine, such as would be calculated from the velocities of the ta- 
bles, and to make the rest of the pipe larger. The greater the 
distance the steam has to pass, the larger should be the pipe. 
To prevent the loss of heat growing out of the increased sur^ 
face, the metal might be kept bright, in which state it will be a 
bad radiator of heat ; but this method is not applicable in prac- 
tice. The steam pipes are, therefore, often covered with a bad 
conductor of heat. 

The principles for calculating the area of the orifice by 
which such pipes communicate with the engine, and the sur- 



94 BOILERS. 

faces of safety valves, are therefore identical ; we shall, in order 
to render them more intelligible, reduce them to the form of a 
Rule. 

To find the area of the passage by which steam shall reach 
the engine from the boiler in which it is generated : 

Divide the quantity of water in cubic inches evaporated 
per hour, by 3600, (the number of seconds in an hour,) multi- 
ply the quotient by the volume of steam of the given tempera- 
ture, from the table on page 24 : This ivill give the num- 
ber of cubic inches of steam that must pass per second. Di- 
vide this by the velocity per second, taken in the cases of high 
steam pipes, from the table on page 73, and in the case of 
low steam pipes from the table on page 93. The quotient is 
three-fourths of the required area, v)hence the diameter of 
the circular section can be obtained in the usual manner. 

Cylindrical boilers, placed in a vertical position, and having 
internal fireplaces and flues, have been much used in the United 
States. In our first edition we noticed one planned by Gol. 
Miller of Charleston, S. C. ; but of this we have seen but a sin- 
gle instance, and it has not come into use. The most familiar 
case of this sort is in the locomotive engines of the Baltimore 
and Ohio Rail -road. We deem it due to justice to state, that 
Mr. John Stevens, of Hoboken, communicated to us, some 
years since, a plan of a boiler on similar principles, that we do 
not doubt would have been equally efficacious. 

In the use of anthracite coal, blowing engines to excite the 
combustion have been found advantageous. Such engines 
have also been applied to other kinds of fuel. In locomotive 
engines, the steam, after it has completed its action, is permitted 
to escape into the chimney, and by forcing out the air in its ra- 
pid expansion, acts to cause a more intense draught, and is thus 
superior to the best blowing engines. 

58. Besides boilers of the various kinds we have mentioned, 
Mr. Perkins proposed one upon very different principles, 
which, for the sake of distinction, is called a Generator. It is a 
strong vessel, completely filled with water, which is heated to 
a very high temperature, and prevented from being converted 



BOILERS. 95 

into steam by the strength of the vessel and the pressure upon 
its safety valve. A small quantity of water is flashed in from 
a forcing pump, which causes the escape of an equal quantity, 
that is instantly converted into steam of high temperature and 
consequent elasticity. As it is our intention to confine our- 
selves to forms that have actually come into general use, and 
as the generator of Perkins is still a subject of experiment, it 
does not enter into our views to describe it more particularly. 

For the same reason that we do not dwell upon the genera- 
tor of Perkins, we shall pass, with a slight notice, the boiler in- 
vented by Bennett of Ithaca, N. Y. In this thefuel is placed in a 
tight chamber furnished with two valves. Through one of 
these air is forced in by a blowing engine. The other opens 
into the boiler. Air will, therefore, accumulate in the fire-place 
until, by the joint effect of heat and compression, it assumes a 
tension even greater than that of the steam. It will then make its 
way into the boiler r and join the steam in its action on the en- 
gine. In experiments made with this apparatus, it appeared to 
produce a greater effect with a given quantity of fuel than any 
other boiler. Difficulties of a practical character have hitherto 
prevented its being brought into use. 

On Plate I. will be seen various forms of boilers. 

Fig. 1 and 2, are a longitudinal section and front elevation 
of the low pressure boiler of Watt, together with its furnace. 

a a a a, body of the boiler. 

b, furnace, with its grate, c, ashpit. 

d d d, flues. 

e, man hole, for entering the boiler to cleanse it. 

/, steam pipe, g } steam guage of the form shewn on a larger 
scale at Fig. 7. 

h, safety valve of the form shewn at Fig. 12. 

i, float of the feeding apparatus. 

k k, lever of the feeding apparatus, Z, valve of the feeding ap- 
paratus. 

m, supply cistern fed by the hot water pump of the engine, 
below this is the tube that conveys the water to the boiler, and 
which contains the float n of the self-acting damper, 

o o, pullies of the self-acting damper p. 



96 BOILERS. 

q, feed pipe. 

r r. guage cocks. It has been already mentioned that this form 
is now but rarely used, and, with its apparatus, is rather a mat- 
ter of history than a model to be copied in the existing state of 
the steam engine. 

Fig. 3, is a transverse section of a cylindrical boiler, the same 
letters are employed to designate such of the parts as are repre- 
sented. When used for low steam, all the parts represented in 
the preceding figures may be applied with equal facility to it. 
The faint circle within shews how the return flues might be 
made to pass through this boiler. 

Fig. 4, is a cylindrical boiler, with internal furnace and flues. 

On PI. VII. may be seen an outside view of a low pressure 
boiler for a steam boat ; this has an interior furnace and flues. 

On PL VIII. is a plan and section of an English steam boat 
boiler. 

On PL VI. are end views of a pair of cylindrical boilers for 
a high pressure engine. 

Perhaps the most perfect form which has yet been given to 
boilers, is that now adopted almost universally in locomotive 
engines, and which we have more than once referred to. The 
body of the boiler is cylindric. One of its ends rises no higher 
than the level of the water in the boiler, and forms the back of 
a furnace, in which by the prolongation of the plates of the 
boiler, the fuel is surrounded by water, except towards the 
ashpit. The flame and heated air are conveyed through the 
boiler in a number of pipes. In fixed engines, they are so 
much more costly than those of the form of a simple cylinder, 
as to be inapplicable • but wherever it is important to save both 
room and weight, they are to be preferred to all others. They 
are, therefore, not only in general use upon rail-roads, but 
have been much employed in American steam boats. 

An outside view of a locomotive boiler may be seen on Plate 
IX. 

Having thus explained the structure of the boiler, and of the 
various accessories with which it may be furnished in order to 
render its action more regular and safe, we shall next proceed 
to treat of the action of steam as a mover of machinery, and of 
the different forms of engine that are at present in use. 



CHAPTER IV. 



GENERAL VIEW OF THE DOUBLE-ACTING CONDENSING 

ENGINE. 

Of Prime Movers in general. — Principles of the action of Ma- 
chines. — Modes of applying /Steam as a prime mover. — ■ 
Application of Steam to the Double-Acting Condensing 
Engine. — Modes of removing Water of Condensation and 
Vapour. — Modes of changing the reciprocating Rectilineal 
Motion of the Piston Rod into a reciprocating circular mo- 
tion. — Method of changing the reciprocating circular mo- 
tion into a continuous one. — Mode of regulating the vary- 
ing motion of the Engine, and making it produce one with 
uniform velocity. — Other methods of obtaining a rotary mo- 
tion. — Effect of the joint action of two Engines. — Water 
used to produce condensation. — Water that has been em- 
ployed in condensation applied to feed the boiler. — Manner 
of ascertaining the state of the Vacuum formed by conden- 
sation. — Mode of regulating the supply of Steam. — Accu- 
mulation of Steam in the boiler, and mode of preventing it.— 
Double-acting condensing Engine considered as self-acting . 
— Packing and Cements. — Estimate of the power of the 
double-acting Condensing Engine. — Estimate of the quan- 
tity of water evaporated for each unit of force. — Estimate 
of the supply of water for the boiler. 

59. The agents which we employ for the production of 
mechanical effects through the intervention of machines, may- 
be divided into three classes. 

13 



98 D0UBLE-ACTOG 

1. The muscular force of man and living animals ', 

2. The force of gravity producing the descent of heavy bo- 
dies, whether solid or fluid ; 

3. Heat, applied either to change the volume of bodies that 
do not change their mechanical state during its action, or to 
convert bodies into elastic fluids,, acting with a powerlul ex- 
pansive force. 

To the second of these classes we refer the force of running 
water, descending in channels to find the lowest accessible le- 
vel ; to the third, the currents of the atmosphere or wind, the 
more powerful agency of inflamed gunpowder, and of liquids 
converted into steam. 

60. Machines are instruments by which we change the di- 
rection or intensity of the moving force. They can all be re- 
duced to six simple forms, called Mechanic powers, and these 
again to two still more simple modifications. In their action 
there is but one principle involved, which is as follows : The 
product of the moving force, estimated in some conventional 
twit, into the space through which the point to which this 
force is applied, is, in all cases, equal to the sum, of the pro- 
ducts of all the resistances i?Uo the spaces described by their 
respective points of application. 

This principle has two distinct cases ; in the first, the ma- 
chine is at rest, or in equilibrio, under the action of the power 
and the resistances. In this ease the points of application must 
be supposed to move, and the space employed in the calcula- 
tion is that through which they woald move without altering 
the conditions of equilibrium. The principle is, in this case, 
called that of Virtual Velocities. In the second case the ma- 
chine moves with uniform velocity under the action of the op- 
posing fomes, and is said to have attained a state of permanent 
working, or to be in dynamical equilibrium. 

A machine passes from the stare of rest, in consequence of the 
conditions of equilibrium being violated, and of the moving 
power acquiring, in consequence, a preponderance over the re- 
sistances. It leaves the state of rest gradually, and therefore 
moves at first with accelerated velocity, the conditions of equi- 



CONDENSING ENGINE. 99 

librium, so Ions: as this acceleration is going on, no longer hold 
good; and there is one casein which the acceleration might 
continue as long as the motion. This is when the moving 
force is capable of acting with equal intensity upon a body at 
rest and upon a body in motion. Of the three classes of forces 
we have mentioned, gravity is the only one that thus acts, and 
it is limited by the check which the motion meets, in conse- 
quence of the body acted upon reaching the solid mass of the 
earth, the resistance of which speedily brings it to rest. But, 
even in the case of this force, the bodies which are propelled by 
it meet with resistances, that may finally render their motion 
uniform. Thus a stream of water, although propelled by the 
force of gravitation, moves in a pipe or channel of constant 
section with uniform velocity. In a! I other cases the action 
of the moving force does not depend upon the velocity with 
which the body in which it resides moves, or has a tendency to 
move, but upon the difference between this and the velocity of 
the machine to which, it is applied. Hence, when the point of 
application is at rest, the force acts upon it with the whole in- 
tensity it is capable of exerting : but when this point has a ve- 
locity equal to that of the body through which the force acts, 
the former no longer receives any impulse from the latter. As 
the motion grows out of the superiority of the moving force, and 
as the action of this force diminishes with every increase of the 
velocity of the point to which it is applied, equilibrium between 
its action and that of the resistances must again take place, and 
if they both act upon a machine, it will assume a state of perma- 
nent working. 

We have used the term resistance ; for the machine must not 
only do the work for which it is constructed, but must also 
overcome retarding forces that exist in the very nature of ma- 
terials and workmanship, or which grow out of extrinsic caus- 
es. Friction is the retarding force from which no material is 
free, and which no perfection of workmanship can wholly re- 
move ; the more important of extrinsic forces is the resistance 
of the fluids, in which machines miy be placed, and which in 
most cases is that of the air of the atmosphere. 

We measure the. mechanical action of a force not merely by 



100 DOUBLE-ACTING 

the weight it is capable of raising, but by the space through 
which it raises that weight in given time. Hence, as the pro- 
ducts of the moving and resisting forces, into the respective 
spaces through which their points of application pass, are equal 
either in the states of ordinary or dynamical equilibrium, the 
measure of these forces is also equal ; and even were there nei- 
ther friction nor resistance from the air, the utmost work a 
moving force is capable of performing, is no more than its own 
measure. Thus nothing is gained by any machine, if consi- 
dered abstractly, while the whole amount of friction and the 
resistance of the air is absolute loss. 

In practice, however, machines are of very great value, in 
spite of this actual waste of moving power : we are enabled by 
them to accommodate the direction of the motion of the agent 
employed to that of the work to be performed ; we can render 
a power that has a fixed and determinate velocity, capable of 
doing work with any other given velocity ; we can apply a 
natural agent, whose intensity is determinate and invariable, to 
overcome a resistance of far greater intensity, although at the 
expense of a loss of velocity ; and we can in either, or all of 
these cases, bring to the aid of the power of man the action of 
the great natural agents, water, wind, and steam. Thus, then, 
the exertion that man must apply, when furnished with proper 
machines to enable him to make use of these great agents, may 
frequently become wholly intellectual, and he will no longer 
have need of his mere physical energies ; or at any rate, a sin- 
gle man will be able to direct the action of a power to perform a 
work, for which the united strength of thousands would be in- 
sufficient. 

It is in the application of steam to machinery, that this tri- 
umph of human mind over matter and the elements is most 
remarkable. 

61. Steam may be applied as a moving power in four dif- 
ferent modes : 

1. It may act against a space, wholly or partially void ; in 
this case, if proceeding from a water of the temperature of 212°, 
it exerts a force equivalent to the difference between the pres- 



CONDENSING ENGINE. 101 

sure of the atmosphere and the tension of the matter contained 
in the space against which it acts ; or, if heated to a higher de- 
gree in a close vessel, with a force corresponding to the in- 
creased temperature, according to the law stated on page 24. 

2. It may be admitted, at a high temperature, into a space 
greater than it is capable of filling at the density that corres- 
ponds to its heat, and act against a space void of air by its ex- 
pansive force. 

3. It may, if proceeding from water heated to a high degree 
in a close vessel, be able not merely to overcome the resistance 
of the atmosphere, but to exert, in addition, a great mechanical 
force. 

Or, 4. It] may cause motion by its re-action. 

In the two first cases it is necessary to have the means to 
form and keep up a vacuum. The mode universally employ- 
ed for this purpose consists in taking advantage of the conden- 
sation of steam itself into a liquid form. By the table upon 
page 24 it appears that the volume of steam at the temperature 
of 212° is 1696 times as great as that of the water whence it 
is generated ; hence, its complete condensation would leave but 
TgVif °f trie space it previously occupied, filled with any ma- 
terial substance. Such complete condensation is indeed im- 
possible, for reasons we shall hereafter refer to ; but it is yet ob- 
vious that a vacuum of a considerable degree of perfection may 
be thus attained. 

The condensation of steam is effected by withdrawing its la- 
tent heat. This is done in the steam engine by the application 
of cold water, that may either be applied to the surface of the 
vessels which contain it, or actually brought into contact with 
the steam itself. In the method now universally adopted into 
practice, the vessel is not only kept cool by immersion in a cis- 
tern of water, but a jet of cold water is constantly flowing into it. 

62. Let a piston be fitted steam tight to a cylinder, closed at 
each end, and let the space both above and below it be filled 
with steam ; if the steam beneath the piston be suddenly con- 
densed, and fresh steam be permitted to flow into the upper 
part, the piston will be depressed to the bottom of the cylinder 



102 DOUBLE-ACTING. 

by the whole energy of the steam, as given in the table on page 
24 ; if, so soon as the piston has reached this lowest position, 
steam be admitted beneath it, and the steam resting upon the up- 
per side be suddenly condensed, the piston will now be forced 
upwards with a force equal to that by which it was caused to 
descend ; after reaching the top, the piston may again be forced 
down, and this alternating aciion may be kept up as long as 
steam can be supplied on the one hand, and the means of con- 
densing it found upon the other. 

If now a rod he passed through a collar in one of the lids of 
the cylinder, and fastened at one of the ends to the piston, this 
rod may be made the means of conveying the force which the 
steam exerts upon the piston, both in its ascent and descent, ei- 
ther directly, or through the intervention of other bodies, to 
some point at which it may be made to perform some regular 
work, or overcome some resistance. 

63. If the steam be condensed within the cylinder, there will 
be a great loss of heat, and consequent increase in the expense 
■of supplying the moving power. Whether this condensation 
be effected by affusion of water upon the outer surface of the 
cylinder, or by the injection of a stream into its interior, the 
temperature of the enclosed space and of the sides of the vessel 
will be lowered, and the heat the steam has communicated to 
them, wholly or partially withdrawn. When the motion of the 
piston is to be reversed, and steam begins to enter on the side on. 
which it was before condensed, it must again heat the piston 
and the adjacent parts of the cylinder up to its own tempera- 
ture ; this it does by parting with its latent heat, and it is con- 
sequently condensed : the steam flowing from the boiler, there- 
fore, exerts no mechanical action until the heat, before abstract- 
ed, is again replaced ; as the piston moves, fresh portions of 
cooled surface are exposed, and fresh quantities of steam must 
be expended in heating them. Such is the effect produced by 
the alternate heating and cooling of the parts, that it has been 
found, by actual experiment, that at least five times as much 
steam is expended upon thern as is necessary simply to fill the 
cylinder. 



CONDENSING ENGINE. 103 

Hence, it is obvious that the steam ought to be condensed in 
a separate vessel, having a communication alternately with the 
upper and lower sides of the piston. 

64. Water is capable of forming vapour at all temperatures 
whatsoever. Its tendency to rise is, however, impeded by pres- 
sure, and thus it does not boil in an open vessel where the ris- 
ing of steam is impeded by the resistance of the* atmosphere, 
until it reaches the temperature of 212°. But with each di- 
minution of pressure, the boiling temperature becomes lower, 
until, in the vacuum of an air pump, it boils at 90° : Hence, so 
soon as a portion of the steam is condensed, fresh vapour will be 
rapidly formed at a lower temperature, and although the ex- 
pansive force of this diminishes in a geometric ratio, yet it is 
still capable of opposing a resistance to the motion of the piston. 
This resistance is such that it has been found by experience 
that the vapour of water of 212°, whose expansive force is equi- 
valent to a pressure of 15lbs. on every square inch, had never 
acted upon the piston with a mean forceof more than lUlbs. until 
means were applied to remove or obviate this resistance. 

It may be removed, or at least very much lessened, by taking 
care to keep up a vacuum in the separate condenser. Two 
modes present themselves for doing this : the engine may be plac- 
ed at least 34 feet above the level of a cistern of water, and the 
condenser may be made to communicate with it by a pipe. As 
that height is the maximum distance to which the pressure of 
the atmosphere can raise a column of water, the water of con- 
densation and the condensed steam will flow into the pipe, and 
as much will pass out at its lower end ; the water being sup. 
ported at a constant level by this pressure. It, however, hap- 
pens so rarely that a proper situation can be found to carry 
this plan into effect, that it has never been applied to practice, 
and has ceased even to be thought of by those concerned in the 
construction of steam engines. 

A pump has therefore been resorted to, in order to keep up a 
vacuum in the condenser, by carrying off the water of conden- 
sation, and the vapour that may remain, or be again generated. 
This pump is called the Air Pump. It may be, with the conden- 



104 DOUBLE-ACTING 

ser, immersed in a cistern of cold water, and a jet of that 
fluid may play through an aperture into the condenser. In this 
manner a greater cooling surface is brought into contact with 
the steam, and the condensation is effected more rapidly than 
could be done by simply cooling the surface of the condenser. 
The water that thus enters is regulated to the working of the 
engine by a valve called the Injection Cock. In some cases, 
however, as in steam boats, a cold water cistern cannot be em- 
ployed. The modifications which the structure of boat engines 
has undergone, will be described hereafter. 

65. The alternating rectilineal motion of the piston in the 
Cylinder of the engine, can of course be only directly applied, 
to perform a work with the same species of motion and with 
equal velocity. Thus, by passing the piston-rod through the 
bottom of the Cylinder, it might be made to work a pump, or 
by laying it in a horizontal position, to drive a horizontal blow- 
ing machine. But the cases where this direct application is 
possible are very few and unimportant, and they have never 
been introduced into practice. Even where a motion of the 
same kind, and with equal velocity, is required, it is the more 
usual custom to carry the motion of the piston-rod to the place 
where the work is to be performed, through the intervention of 
a Balance or Lever beam, resting upon pivots. 

This beam, having the axis that passes through these pivots 
fixed, its ends move in circular arcs with reciprocating motion. 
Now, as the motion of the piston-rod, although reciprocating, is 
rectilinear, it becomes necessary to make the connexion be- 
tween the piston-rod and the beam of such a nature as will 
permit the one of these motions to be accommodated to the other. 

The simplest, and it might almost be said, the most obvious 
plan, is to affix a bar to the end of the piston-rod, at right an- 
gles to its direction, and make the ends of this bar describe 
straight lines, by adapting them to straight guides of iron ; the 
end of the piston-rod being thus kept to its rectilineal course, 
the end of the beam is attached to it by a bar, which has a mo- 
tion upon cylindrical gudgeons, affixed both to the piston-rod 
and the beam. Through this bar the force that impels the rod 



CONDENSING ENGINE. 105 

in its ascent and descent, is conveyed to the beam, and the gud- 
geons allow the bar to change its position in such a way that 
one end may always move in a straight line, and the opposite 
one in an arc of a circle. 

We have said that this method would seem the most ob- 
vious ; it is not, however, the earliest, and has only been 
used in the United States, where it has entirely surperseded 
the earlier method we are about to describe. This method is 
called the Parallel Motion. A bar similar to that we have des- 
cribed connects the piston-rod to the end of the beam, but the 
former has no guides ; a parallelogram is then formed of this 
rod, of a part of the lever-beam, and of two bars equal and pa- 
rallel to them ; the two gudgeons we have mentioned are si- 
tuated at two of the angles of this parallelogram, and at the other 
angles the connexion between the pieces that form the sides is 
also effected by gudgeons or pivots, which are called Centres. 
This parallelogram has therefore sides of a constant magni- 
tude, but the angles are capable of variation in size by the mo- 
tion of the sides upon the centres which connect them. The cen- 
tre at the angle diagonally opposite to that where the end of the 
beam is joined to the bar which connects it to the piston-rod, 
is attached by a bar to an immovable pivot in the frame of the 
instrument, or in an adjoining wall. By this last connexion, 
the point at this last-named angle, will, when the beam oscil- 
lates, describe a circle around the centre of the fixed pivot. 

The points at the two angles of the parallelogram which are 
situated at the end of and upon the beam, will also describe 
circular arcs, whose convexity is opposed to that of the arc 
described by the point attached to the fixed pivot. When the 
radii of these three different arcs bear a proper relation to each 
other, the remaining angular point of the parallelogram will des- 
cribe a straight line. Its path is, in truth, a portion of a curve 
of contrary flexure, but within the limits of the oscillations of 
the beam, it does not differ sensibly from a straight line. But 
as it is not really and truly a straight line, this method, how- 
ever ingenious, is both less perfect in theory and more com- 
plex in practice than the other. The side of the parallelogram 
opposite to that which is a part of the working beam, is called 

14 



106 DOUBLE-ACTING 

the Parallel Bar ; the remaining two sides are called Straps ; 
the bar which connects the lower angle of the parallelogram, 
to which the piston-rod is not fastened, with a fixed pivot, is 
called the Radius Bar. 

We have spoken of the bars, that, with a part of the beam, 
make up the parallel motion, as single. So far as their theory 
is concerned, this is sufficient, but for the sake of a proper ad- 
justment of the pivots, the straps are made double. 

In the pair of straps nearest the fulcrum of the lever beam, 
there is another parallel motion, which is applied to work the 
air pump. This consists in adapting a pivot, to the two straps 
to which the pump-rod is attached, by a circular socket, in such 
a way that the direction of the rod is not changed by the motion 
of the pivot; this pivot, thus placed between two points which 
describe circular arcs convex towards opposite directions, may 
be so adjusted in its distance from each respectively, as con- 
stantly to describe a straight line. The principle of these pa- 
rallel motions will be understood by reference to the following 
description and figure. 

m bis a, part of the lever beam in its lowest position, on being 
the centre on which it vibrates ; to the points a and b are at- 
tached the straps afc and b of, and to these the parallel bar c d ; 
the axis of the radius bar is in a line passing through b, and its 
other end is attached to the point c. The four angles a, b, c, d 
are formed by pivots so as to have a free motion, and the ra- 
dius bar has pivots both at 6 and c. Thus the points a and b 
will, when the beam moves, describe the circular arcs a g i, 
and b I k, while the point c will describe the circular arc c e « } 
whose convexity is opposite to the two former arcs ; and they 
will compel the point d to describe the straight line d b h. In 
this figure the line a 6 is half the length of one arm of the le- 
ver beam, and the radius bar is equal to the same line, but there 
may be other proportions ; all that is necessary, is that the ra- 
dius bar shall be equal in length, between its centres, to the dis- 
tance between the points m and a. 

The second parallel motion is formed by placing a pivot/, at 
the point where the line m d cuts the side a c of the parallel- 



CONDENSING ENGINE. 



107 



PARALLEL MOTION. 




108 DOUBLE-ACTING 

ogram, this point will then be compelled to describe the straight 
line/ an. 

For the parallel motion has recently been substituted the fol- 
lowing arrangement, to which we have already referred as still 
simpler. To the end of the piston-rod is attached a bar, or cross 
head, at right angles to it, the ends of this are placed between 
parallel vertical guides, situated in the plane passing through 
the line d b h. The cross beam is turned, at two places, into 
the form of pivots, to which the straps that unite the piston-rod 
to the working beam are applied. This method has several 
advantages over the parallel motion. It is much more easy of 
construction, and requires no geometric skill in the workmen. 
It is less costly. It, in addition, will permit the beam to describe 
an arc of greater amplitude, and thus the space occupied by the 
engine may be diminished. 

66. The end of the beam, opposite to that which is attached 
to the piston-rod, has also a reciprocating circular motion, ris- 
ing as the other end falls, and falling as it rises. This species 
of motion is hardly adapted to be applied directly to any usual 
species of work. In most of the important applications of the 
steam engine, the required motion is circular and continuous. It 
hence becomes necessary to convert the reciprocating motion 
of the working end of the beam into the last-named variety of 
motion. This change is effected by the intervention of the 
Connecting Rod or shackle bar, and the Crank. 

The connecting rod is a bar of iron attached to the working 
end of the lever beam by a cylindrical pivot, and a circular 
socket, in which it has a free motion. The crank is an arm or 
radius of iron, having a pivot at each end, one of these is fixed in 
a horizontal position to a socket in a solid support, and the arm 
has a free motion around the axis of this pivot ; the pivot at the 
other end projects from the arm, and is inserted in a socket on 
the lower end of the connecting- rod. The length of the crank 
between the axes of the two pivots is equal to half the space 
passed through by the piston in the Cylinder, or what is called 
the length of the stroke. It is at least so when the arms of the 



CONDENSING ENGINE. 109 

beam are of equal lengths, as is most usually the case ; and 
when they are not, this distance has the same ratio to half the 
leno-th of stroke as the arms of the beam, to which the connect- 
ing rod and piston are respectively attached, have to each other. 
The working end of the beam, rising and falling in a circular 
arc, under the impulse conveyed from the Cylinder through 
the parallel motion, will act upon the crank through the inter- 
vention of the connecting rod ; the moveable end of the crank 
will describe, under this influence, a semicircle during the time 
that the beam either rises or descends : this semicircle may be 
directed to either side of the vertical line passing through the 
axis of the crank ; and a slight force applied to it in a proper 
direction, at its highest or lowest positions, will cause it to de- 
scribe a complete circle. 

This apparatus may be better understood by reference to 
Fig. 5, on PI. IV, where A represents the end of the lever 
beam, b the part of the connecting rod, which is forked at the 
end, and embraces the beam ; c, the connecting rod represented 
in its highest position ; d, the pivot on the crank to which the 
connecting rod is attached ; E, the arm of the crank of which 
f is the centre ; g, h, i, k, represent four other positions of the 
crank. 

67. The force that renders the rotary motion of the crank 
continuous, is derived from the fly-wheel, which also fulfils 
another most important purpose. 

No motion can well be imagined more irregular than that of 
the piston of a steam Cylinder. When it is in contact with ei- 
ther end of the Cylinder, the entrance of the steam gradually 
impels it from a state of rest, until it acquires a maximum of 
velocity, whose magnitude depends upon the relation between 
the supply of steam and the work to be performed. When it 
reaches the opposite end of the cylinder it again comes to rest, 
more or less suddenly, according to the manner in which the 
steam is supplied and cut off. A motion in the opposite direc- 
tion next succeeds, gradually increasing at first, and again ceas- 
ing when the piston reaches the opposite limit of its motion. 
It will be thus seen that not only is the direction of the mo- 



110 



DOUBLE-ACTING 



tion alternating, but that its velocity is continually varying, and 
that at two instants there is no motion whatever. Now, in 
very many applications of steam, it is not only necessary that 
the action be continuous and circular, but that its rate should 
be uniform. To effect these two objects, advantage is taken of 
the nature of matter, which has not the power either of setting 
itself in motion, or bringing itself to rest ; hence, when a mass 
is once set in motion, it will have a tendency to move forward 
continually, and with uniform velocity ; this it will tend to do, 
although the force that set it in motion cease to act ; and if its 
motion be resisted, the moving mass will communicate motion 
to the bodies which oppose it. The part of a machine in which 
this principle is called into action, is called a Fly-Wheel. It is 
usually a heavy circular ring, attached, by radiating arms, to the 
axis of a part of the machine that has a rapid motion. In steam 
engines it is fixed to the axis of the crank. The fly-wheel, 
like every other part of a machine, opposes a resistance to the 
moving power, and requires a certain expenditure of force to 
set it in motion ; but when once it is set in motion, it requires 
but small accessions of force, and these may be exerted at in- 
tervals, to keep it moving with the greatest mean velocity which 
the moving power, acting through the intervention of the ma- 
chine, is capable of communicating. If the power be variable, 
and therefore haveatendency to cause irregularity in themotion 
of the machine, the fly-wheel resists acceleration, on the one 
hand, because it cannot suddenly acquire a new velocity ; but 
will oppose any increase with a force equivalent to the product 
of its mass into the difference between the velocity it has when 
the acceleration begins to act, and that which the accelerating 
force is capable of giving ; on the other hand, as its motion 
cannot be suddenly checked when the force is either lessened 
or ceases to act, it therefore goes on, with a velocity decreas- 
ing only in consequence of the resistances it meets. In parting 
with its motion, it will communicate as much to the bodies 
which resist it, and will thus keep up the velocity of the ma- 
chinery driven by the engine, and render that of the engine itself 
regular until the acceleration again commences. Hence, in the 
varying action of the piston of a steam engine, the fly-wheel 



CONDENSING ENGINE. Ill 

moderates the speed -when it has a tendency to become greatest 
receiving then an accession of force ; this it distributes again 
among the parts of the machine that are in motion, when the 
speed of the piston lessens, or actually becomes nought, which 
happens when it reaches its highest and lowest points. If the 
mass and velocity of the fly-wheel be made great, this tenden- 
cy to uniformity will become absolute, and it will go on with 
uniform velocity, under the constant variation of the motion 
originally received from the prime mover, giving to the machi- 
nery driven by the steam engine a regular and constant velo- 
city. This tendency of the fly-wheel to go forward with con- 
tinuous rotary motion, accelerated at first until it reach a mean 
between the maximum and minimum velocity which the piston 
is capable of communicating to it, through the intervention of 
the parallel motion of the working beam and the crank, is attain- 
ed by its passing through a single semicircle, or by performing 
no more than half a revolution ; hence, when the piston 
reaches its upper or lower position, and the steam ceases for an 
instant to act, the fly-wheel carries the crank forward beyond 
the vertical line ; the new impulse derived from the steam when 
it acts on the opposite side of the piston, is exerted to compel 
the crank to move forward in the opposite half of the circle it 
before described, and therefore with continuous rotary motion. 
The form and mode of action of the crank has a very benefi- 
cial influence, in permitting the uniform motion of the fly to be 
attained without exerting any injurious action upon the engine 
itself. The force of the crank is always applied to the fly- 
wheel, in the direction of a tangent to the circle the crank it- 
self describes ; the force of the steam acts upon the crank in 
the direction of the connecting rod. When the force of the 
steam is nothing, in consequence of the piston being in the act 
of changing the direction of its motion, these two lines are at 
right angles to each other ; the crank may therefore be carried 
forward by the fly-wheel, without being interrupted by the ab- 
solute cessation and subsequent change in the direction of the 
motion of the piston. But when the steam is exerting its 
maximum force upon the piston, these two lines nearly coincide, 
and the crank receives the whole force of the steam. Among 1 



112 DOUBLE-ACTING 

all the modes, therefore, by which a variable and alternating 
motion is converted into one that is continuous, none is more 
advantageous than the crank, and few as much so. One, 
which will be mentioned in the history of the Steam Engine, 
has equally good properties in this respect, and we know of no 
other. 

Persons ignorant of the principles of mechanics are in the 
habit of considering and declaring that much power is lost 
when motion is conveyed through the intervention of a crank. 
This idea appears to have been originally founded upon what 
occurs when a man works by means of a winch, an apparatus 
similar to a crank, and acting upon the same principles. Here 
a power which, when constantly and directly exerted, is capa- 
ble of balancing a pressure of 70lbs., is not capable of overcom- 
ing a resistance of more than 251bs. This, however, arises 
from the force itself actually falling, during one part of the re- 
volution of a winch, as low as the last-named limit ; and hence 
the revolution cannot be completed if the constant resistance 
exceed that amount. The power of a man depends not only 
upon his muscular force, but upon the manner and direction in 
which that muscular force is exerted ; and in some parts of the 
motion of a winch, this manner is extremely unfavourable. 
The crank or winch still acts upon the resistance, with the 
whole force the man applies to it, but this is less at some parts 
of the revolution that it is in others. In the steam engine, a 
similar variation in the intensity of the prime mover occurs, 
and it is greater in amount ; but while a man is as much, and 
even more fatigued in applying his force in the unfavourable 
positions of the winch, the varying motion of the piston of the 
steam cylinder corresponds almost exactly with a variation in 
the expenditure of steam. 

As a general principle in mechanics, no force can be lost ; it 
may be applied to resistances which do not enter into the esti- 
mate of the work performed ; for instance, to overcome the fric- 
tion of the machine ; or it may, by improper or disadvanta- 
geous direction, be wasted upon the machine itself, whose parts 
it thus tends to tear asunder or wear away. This last circum- 
stance does occur in the action of a steam engine, such as we 



CONDENSING ENGINE. 113 

have described it, but the crank is not the only part which is 
liable to this objection. The rod or strap, which forms a part 
of the parallel motion, does not always act in the direction of a 
tangent to the arc described by the end of the working beam, 
with which it is connected. Hence, it at times expends a part 
of the force of the engine upon the beam, tending to draw it 
from its place. A similar obliquity occurs where the connect- 
ing rod is attached to the opposite end of the beam, and a simi-* 
lar waste of power. In the crank, the connecting rod acts upon 
it at all angles with its tangent, from 0° to 90° ; and hence a 
part of the force is wasted to draw the axle of the crank from 
its seat. Were the force of the steam constantly exerted upon 
a connecting rod three times as long as the stroke of the engine, 
the power thus wasted would bear to the whole power of the 
steam the proportion of 0.225 to 1, but as the steam actually 
ceases to exert any force at the upper and lower points of the 
crank's revolution, here no loss can occur, and the waste can- 
not exceed the ratio of 0.139 to one, or about one-seventh part ; 
while, if, as usually happens, the pressure of the steam first 
gradually increases, and then again diminishes, the real waste 
need not exceed one-tenth part of the force of the engine. A 
longer connecting rod causes the power to act more directly, and 
its waste to be consequently less. 

This waste is less than the friction of the engine, and still 
less than the increase the friction would acquire in any of the 
methods that have yet been proposed, of making the steam act 
directly upon a body so disposed as to be capable of acquiring 
a rotary motion, instead of applying it to a piston working with 
alternate strokes in a cylinder. We are therefore disposed to 
think that most of the plans which have been hitherto proposed 
of constructing rotary engines, have been a sheer waste of inge- 
nuity. 

68. The method we have described, of converting the alter- 
nating motion of the piston-rod into a continuous rotary one, 
through the intervention of a parallel motion, a working beam, 
a connecting rod, and a crank, is not universal. The change is 
sometimes effected more immediately by affixing the connecting 

15 



114 DOUBLE-ACTING 

rod to a cross-head on the end of the piston-rod, which is then 
made to work between guides. When the Cylinder is ver- 
tical, the connecting rod and crank are usually double, the for- 
mer descending on each side of the Cylinder. We have seen 
more than one plan, in which the Cylinder itself was suspended 
upon trunnions, permitting it to have a vibratory motion. In 
this last form the connecting rod may be dispensed with, and 
the piston-rod acts immediately upon the crank. The steam is 
admitted to the Cylinder through the trunnions. Such was the 
condensing engine of French, placed in a boat on the Hudson 
river in 1808, and such is the high pressure engine construct- 
ed recently by an ingenious workman in the employ of the West 
Point Foundry ; and which, since the first edition was publish- 
ed, has been used both in stationary and locomotive engines 
constructed at the Novelty Works, New- York. This mode of 
suspension is, however, only suited to small engines, where the 
Cylinder has but little weight. When the beam is suppressed, 
there results a very considerable saving of room, and there are 
occasions where this is very important. An engine which has 
no beam, will occupy a space whose length is less than half that 
taken up by one that has. Tn many of the American steam 
boats, and particularly in most of those constructed under the 
direction of Fulton, the engine has this form. In the Western 
States, it is usual not only to suppress the beam, but to lay the 
cylinder in a horizontal position. This last method has many 
advantages, among which may be mentioned as the principal, 
that a vessel is far less injured by a force acting in the direction 
of its length, than by one exerted vertically ; and that the en- 
gine may be laid entirely under deck without interfering with 
any of its more valuable properties. 

On the other hand, the suppression of the working beam has 
this disadvantage, that the obliquity of the action of the piston 
upon the connecting rod is greater than occurs when the pa- 
rallel motion and beam are used : and that the loss growing out 
of this obliquity is greatest in proportion to the power when 
the latter is a maximum ; hence, the waste, compared with the 
mean power, is greater than in the other case. This, however, 
does not apply to Cylinders hanging upon trunnions, for, in 



CONDENSING ENGINE. 115 

them, the power is applied directly when at its maximum of 
intensity. 

69. In some few cases the motion communicated to the fly- 
wheel is rendered more uniform by using two complete en- 
gines, whose cranks are adapted to the same axle, but are situ- 
ated in planes at right angles to each other. When the piston 
of one of these Cylinders has reached the top or bottom, that of 
the other will be in the middle of its stroke. One of them will, 
therefore, be acting at its maximum of force when the other 
ceases to act altogether. This plan is far preferable in effect to 
that of a single engine of the same nominal power, but it is more 
expensive, as a single engine of twice the force of each of them 
costs considerably less than the two. In many of the best loco- 
motive engines this method has been successfully used ; but 
when two engines are applied to a boat, it has been found that 
it was difficult to keep them at the same rate of working ; hence 
each is now usually applied to a separate shaft, and moves only 
one of the wheels. In the British steamers, however, the two 
engines act at right angles to each other upon the same axle. 

A fly-wheel is not always an indispensable part of an engine, 
for there may be some of the machinery which is driven, that 
will act as a regulator in its stead. Thus, in steam-boats 
where the wheels have a rapid motion, and in rail-way car- 
riages, no fly-wheel need be employed. 

70. The condensation of the steam is effected in the Condens- 
er, both by keeping it constantly cool, and by admitting a jet 
of cold water into that vessel. To accomplish these objects, 
it is wholly immersed in a cistern supplied with cold water ; and 
a stream constantly spouts through an aperture in the side of 
the condenser, to which a stop-cock is adapted ; the quantity of 
this stream is regulated by the greater or less aperture which the 
stop-cock affords for the passage of the water. Steam at 212°, 
is capable, as may be inferred from what has been stated on 
page 21, of heating six times its weight of water to the same 
temperature, and the united bulk is seven. The temperature 
of condensation is usually 100°, and to cool seven measures of 



116 DOUBLE-ACTING 

water of 212° to 100°, will require about sixteen measures of wa- 
ter, which, added to the six employed in condensation, is twenty- 
two. That is to say, twenty-two times the bulk of water eva- 
porated by the boiler, is the least quantity that will suffice for 
the proper condensation of steam, and cooling the condensed 
water. There must, besides, be a supply to prevent the water 
of the cistern from growing warm ; and it has hence been usual 
to make the cold water pump capable of supplying a pint of wa- 
ter for every cubic inch evaporated from the boiler. 

71. In order to save a part of the heat, the condensed steam 
and water of condensation are delivered by the air pump into 
a vessel called the Hot Water Cistern, whence the water is rais- 
ed, by the Hot Water Pump, to the feeding apparatus of the 
boiler. These two pumps are worked by rods, attached to the 
working beam, when the engine has one ; in other cases these 
rods, with the rod of the air pump, are attached to a bar or 
beam, one end of which is adapted to the piston-rod, and rises 
and falls with it ; the other is fastened to a fixed centre upon 
which it oscillates. 

72. The power of a condensing engine depends upon the 
state of the vacuum that is kept up in the condenser, as well 
as upon the pressure of the steam flowing from the boiler ; 
hence it is important to be able to know whether the rarefac- 
tion produced by the condensation of the steam, and the action of 
the air pump, be more or less perfect. This knowledge is at- 
tained by the Vacuum Gnage. A glass tube, open at both ends, 
has its lower extremity immersed in a basin of mercury, the 
other end communicates by a pipe with the interior of the con- 
denser. When the steam is condensed in that vessel, the 
pressure of the atmosphere forces the mercury to rise in the 
tube to a height which is the measure of the exhaustion ; the 
difference between the height of this column and the height 
at which the mercury stands in a barometer, is the measure of 
the force which acts in opposition to the pressure of the steam 
upon the piston of the engine. This must, therefore, be deduct- 
ed, in estimating the actual performance of the engine, from the 



CONDENSING ENGINE. 117 

indications of the steam-guage after an atmosphere has been 
added to the latter. An apparatus called the Indicator, in which 
a spiral spring is alternately opposed to the steam and the va- 
cuum, has been proposed as a substitute for both the Steam and 
Vacuum Guages ; but it has not yet come into general use. 

It is, however, the only apparatus by which a true estimate 
can be obtained of the force actually employed in a steam engine, 
and, when compared with the steam and vacuum guages. would 
illustrate that part of the theory which is yet deficient, namely, 
the determination of the pressure which is exerted by steam of 
a given tension upon a piston moving with a given velocity. 

73. The action of the fly, in producing regularity of motion, 
reaches only to the inequalities that take place in the motion of 
the piston during a single stroke. Should the flow of steam 
increase, the mean motion of the fly-wheel will be accelerated, 
and, should the flow be diminished, the fly-wheel will be uni- 
formly retarded. Neither does it control any change in the mo- 
tion of the machinery, driven by the steam, unless that change 
be periodic. But it frequently happens that the quantity of 
steam supplied by the boiler, fluctuates. Some regulator is 
therefore necessary, whenever work is to be done with regulari- 
ty, which shall control the prime mover itself. For this pur- 
pose a Governor is adapted to the steam engine. This is also 
required in cases where the quantity of work to be performed is 
fluctuating, as is the case in many branches of manufactures, 
where a part of the machinery may be suddenly stopped, or 
may be as suddenly connected with the engine. The govern- 
or is an apparatus that is sometimes called a Conical Pendu- 
lum. Two heavy balls are suspended by bars to the opposite 
sides of a vertical axis. This axis is set in motion by the en- 
gine ; as it turns, the balls of the governor acquire a centrifugal 
force, which may be sufficient to overcome their weight, and 
cause them to diverge and fly off, performing in their course a 
larger circle than before. As the balls fly off, they act, through 
the intervention of a system of levers, upon a valve that is si- 
tuated in the steam pipe. This, which is called the Throttle- 
valve, has the form of a circular disk of metal, exactly filling 



118 DOUBLE-ACTING 

up the pipe whan placed across it. It turns upon pivots placed 
at the opposite ends of one of its diameters, and may thus 
either present its edge to the steam that passes along the pipe, 
in which case it hardly resists its course ; or may assume any 
intermediate position until it close the pipe altogether. When 
the balls of the governor revolve with so little velocity that the 
centrifugal force cannot overcome their weight, the levers place 
the throttle valve in the position that presents its edge to the 
steam ; when the velocity becomes great enough to throw out 
the balls to their utmost limit, this valve is thrown across the 
pipe, and shuts the passage completely ; with intermediate po- 
sitions of the valves, the passage is more or less open, accord- 
ing to the rotary velocity of the governor. 

The governor is driven, by a strap that passes over a drum 
on the axis of the crank, or by wheels and pinions, deriving 
their motion from the same part of the engine. This apparatus 
is of no use in navigation or locomotion, but is indispensable 
in engines used for manufacturing purposes. 

74. When the throttle valve acts under the influence of the 
governor to lessen the efflux of steam from the boiler, the elastic 
fluid will accumulate in that vessel, and its density and elasticity 
will increase along with its temperature. In this event it will 
act upon the float which counterpoises the self-regulating damp- 
er, and the latter will descend and lessen the draught of the 
chimney. A diminution in the expenditure of steam thus acts 
to diminish the intensity of the fire by which it is generated, 
while, if it accumulate too suddenly, the safety valve affords it 
a vent. 

It is, however, to be remarked, that such floats are inadmissible, 
except when the tension of steam does not much exceed a sin- 
gle atmosphere ; and that self-regulating dampers are never used 
in steam-boats or locomotive engines. 

The valves, by which steam is admitted into the upper and 
lower parts of the cylinder alternately, and by which the com- 
munication with the boiler is opened and closed, are worked by 
machinery attached to the engine. Rack work upon the rod 
of the air-pump was originally used for this purpose, but it is now 



CONDENSING ENGINE. 119 

more usual to adapt an Eccentric to the axle of the crank. The 
eccentric is a circular plate of metal, which has an opening 
within it that just fits a part of the axle of the crank. This open- 
ing is placed in a position eccentric to the plate itself, and hence 
the apparatus derives its name. The eccentric plate is attach- 
ed to the axle of the crank, and revolves with it. A circular 
ring fits upon the eccentric, but leaves the latter a free motion 
within it ; any given point in this ring will, therefore, have its 
distance from the axis of the crank changed within certain lim- 
its ; this change is conveyed to a bent lever which works the 
valves, through the intervention of an open frame-work of the 
figure of an isosceles triangle, whose two equal sides are tan- 
gents to the circular ring that encloses the eccentric plate. 

75. The Double-Acting Condensing Steam Engine, then, is 
in a great measure self-acting. In truth, when applied to per- 
form work with an uniform velocity, little is left to be done, ex- 
cept to supply the fire with fuel, and to observe the indications 
of the guagesfrom time to time. Even the supply of fuel has been 
regulated by machinery driven by the engine, in such a way 
that it need not be fed for several hours. It is therefore not to 
be wondered that the condensing steam engine, worked by steam 
of a tension little exceeding an atmosphere, was considered for a 
time, and is still considered by many, as the most perfect of all 
human inventions. We shall, however, have occasion to des- 
cribe another method of working the condensing engine, by 
which its efficient power has been more than quadrupled. It 
unluckily happens that much of the beautiful and ingenious ap- 
paratus which, in their application to the engine or the boiler, tend 
to render the former self-acting, are rendered useless in the 
new mode of working. 

76. The pistons of the Cylinder and air-pump, and the open- 
ings in the covers of those parts of the engine through which they 
move, are rendered steam tight by packing. The substance for- 
merly solely employed for this purpose was hemp, in the form of 
plaited bands, and it is coated with grease. The joints of the se- 
veral parts are closed by plaited hemp, or felt, coated with white 



120 DOUBLE-ACTING 

lead ground in oil, or where one part is made to fit into another, 
by an iron cement, composed of iron filings, or gun borings, mu- 
riate of ammonia, and flour of sulphur ; the proportions are 
sixteen parts by weight of the first, two parts of the second, and 
one of the third substance. The joints are, generally speaking, 
formed by flaunches cast upon the pieces, in which holes are 
drilled ; through the latter are passed screw bolt?, that are fasten- 
ed by nuts. 

The power of machines is estimated in terms of some con- 
ventional force, taken as the unit. Steam engines having been 
originally introduced as a substitute for the action of horses, it 
became the practice to compare the force of an engine with the 
strength of a number of horses. The unit, which is employed 
in the estimate, is, therefore, a horse-power ; and we speak of 
engines as being of the power of a certain number of horses. 
As the strength of horses is very various, this is still a vague 
method, and it becomes necessary that the estimate of the work 
a horse is capable of performing, should also be agreed upon. 
Different engineers have at different times made use of different 
values ; but the modes of estimating the horse-power resolve 
themselves into the expression of the number of avoirdupois 
pounds raised one foot high in a minute. 

Desagnliers estimates this number at 27,5001bs., and Smea- 
ton 22,9161bs. Watt supposes that a horse is able to raise 
32,0001bs. ; but in calculating the power of the engines of Watt 
and Bolton, the estimate has been taken as high as 44,0001bs. 

The force which acts is the pressure of the steam, and as 
much pressure as is indicated by the steam guage is supposed 
to act upon the piston ; this, multiplied by the velocity of the 
piston, gives the whole power of the steam ; but before the steam 
that issues from the boiler can reach the piston, it is retarded by 
the friction of the pipes, and loses by cooling a part of the ex- 
pansive force indicated by the steam-guage ; its action is next 
diminished by the cooling it undergoes in the Cylinder itself; 
and before the power is transmitted to the working point of the 
engine, it must overcome the friction of the piston, open and 
shut the valves, force the steam into the condenser, and work 
the air-pump and the hot and cold water pumps. It has, next. 



CONDENSING ENGINE. 121 

to overcome the friction of the axles of the lever-beam, parallel 
motion, and crank ; and the piston is besides resisted by the 
uncondensed steam remaining in the condenser. Of the last, 
the vacuum guage furnishes a measure ; but of all the rest no- 
thing is known perfectly, except by comparing the work ac- 
tually performed with the original force of the steam. 

We have further to remark, what appears to have been neg- 
lected by all former writers, that the actual tension of the steam 
is not the measure of its pressure upon the piston when in mo- 
tion. It will be obvious that the whole of such a force can 
only be exerted upon a body at rest, and that when the velocity 
of a body is as great as that with which the steam can fol- 
low it, all pressure ceases. It might be a mathematical inves- 
tigation of no little theoretic interest to determine at what ve- 
locity within these limits a maximum effect is produced, and 
what will be the pressures of steam of a given tension upon a 
piston moving with given velocities. It does not, however, seem 
probable that at the present moment such an investigation 
would be attended with any valuable practical result. 

It has been deduced from observation upon the working of 
engines, that more than 40 per cent, of the original power of 
the steam is lost from these several causes ; hence the indication 
of the steam-guage must be diminished in that ratio at least, 
before it is employed in the calculation of the force of the en- 
gine. 

In this country it has been usual to estimate the horse power 
at 33,0001bs., raised one foot per minute, and the mean pres- 
sure of the steam, in a condensing engine, at lOlbs. per square 
inch. We hence have the following rule : 

Multiply the area of the piston in square inches by 10, and 
by the velocity of the piston in feet per minute ; divide the 
continued product of these three quantities by 33,000, the quo- 
tient of the estimated force of the engine in horse power. 

The rule of Brunton gives 44,0001bs. for the divisor, and 
that of Tredgold reduces the mean pressure to 9,10 pounds 
per square inch, which would correspond to a divisor of near- 
ly 36,000 when the pressure is assumed at lOlbs. The tension 
of the steam is supposed to be five inches of mercury, marked 

16 



122 DOUBLE-ACTING 

by 2\ inches in the mercurial guage ; and equivalent to a pres- 
sure of 2£lbs. more than an atmosphere, or 17^1bs. per square 
inch. The safety valve is loaded with a weight of three 
pounds per square inch, which, with the aid of the atmosphere, 
will retain steam whose expansive force is not greater than 
J 81bs. per inch. 

77. The quantity of water to be evaporated in order to do the 
work of a horse in a double-acting condensing engine regu- 
lated as we have just stated, may be estimated as follows, viz : 
A cubic foot of water, evaporated under the ordinary pres- 
sure of the atmosphere, occupies a space 1696 times as great 
as it did before ; but the space it occupies under a pressure of 
17| pounds is, if we abstract from the expansion by tempera- 
ture, less in the ratio of 15 to 17| ; for elastic fluids occupy 
spaces inversely proportioned to the pressures by which they 
are confined, (see p. 14); hence the space occupied by steam 
having an expansive force of 17|lbs. is 1454 times the original 
bulk of the steam. 

A cubic foot of water, therefore, occupies a space, in the form 
of such steam, of 1454 cubic feet ; and the effective pressure, 
as we have before stated, is lOlbs. per square inch, or ]4401bs. 
per square foot ; the power of a cubic foot of water is, therefore, 
to lift 1440x1454 or 2,0937601bs. through the space of a foot. 
If this be divided by 33,000, which is the conventional weight 
to be lifted by a horse power per minute, it will give the num- 
ber of minutes in which, if a cubic foot of water be evaporated, 
it will keep up this conventional unit of force. The quotient is 
63, or three minutes more than an hour. It is therefore usual 
to allow the evaporation of a cubic foot of water per hour to 
be equal, in the engine under consideration, to a horse power ; 
and as it is well to be always certain of a supply of steam, 
boilers are made to furnish more units of steam than the en- 
gine is estimated at ; the waste of heat in small boilers being 
greater in proportion than in large ones, this excess is a con- 
stant quantity, the boiler being calculated to produce steam 
equivalent to two horse power more than the estimated force 
of the engine. We have seen that a surface of boiler in con- 



CONDENSING ENGINE. 123 

tact with flame and hot air of 8 square feet (see p. 57) is equal 
to the conversion of this quantity of water into steam. 

78- The feeding apparatus of the boiler, which is, in this form 
of engine, composed of a pump that raises the water of conden- 
sation from the hot water cistern to a cistern at the top of the 
feed pipe, must therefore supply at least one cubic foot per 
hour for each horse power at which the force of the engine is 
estimated : or 1 4 *- 5 4 part by bulk of the capacity of the cylinder, 
at each stroke of its piston. As, however, it is better to have 
an excess than a defect of water, the hot water pump usually 
raises at each stroke - 9 -^oth part of capacity of the cylinder. 

Such are the general principles of action of one form of the 
condensing engine, which, to distinguish it from others in 
which the same operation is employed to form a vacuum, is 
called the Double-Acting Engine, to which epithet is also add- 
ed the name of the inventor, Watt. We are now prepared to 
enter into a more particular view of its several parts, the use 
and operation of which would have been unintelligible, had 
we not previously investigated their uses, and the relation in 
which they stand to each other. 



CHAPTER V. 



DESCRIPTION OF THE DOUBLE-ACTING CONDENSING 
ENGINE. 

Usual form of Double- Acting Condensing Engine. — Steam- 
pipe. — Jacket. — /Side Pipes. — Side Valve. — Puppet Valve. 
— Balance Valve. — Cylinder. — Cylinder Lid. — Cylinder 
Bottom. — Piston. — Woolfs Piston. — Metallic Packing. 
■ — Condenser. — Air Pump. — Delivering Door. — Air Pump 
Bucket. — Hot Water Cistern and Pump. — Cold Water 
Cistern. — Injection Cock. — Water of Condensation.- — 
Cold Water Pump. — Parallel Motion. — Lever Beam. — 
Pump Rods. — Connecting Rod. — Crank. — Fly Wheel. — 
Tumbling Shaft. — Eccentric. — Double Eccentric. — Ad- 
justment of Eccentric. — Governor. — Throttle Valve.— 
Other forms of Double-Acting Condensing Engine. — 
Mode of setting these Engines in motion. 

79. Having in the last chapter explained the general princi- 
ples of action of the Double Condensing Engine, we shall now 
proceed to describe the several parts more particularly, and in 
reference to a plate, on which they are figured in connexion 
with each other. See. PI. III. As the condensing engine, in 
its most complete form, and adapted for general purposes, is in 
more general and frequent use in Great Britain than in this 
country, an engine constructed by Messrs. Murray, Fenton & 
Wood, of Leeds, has been chosen for the illustration of this 
part of our subject 

Fig. I. is an external elevation of this engine. Fig. II. a 
section. Fig. III. a horizontal plan. Fig. IV. a view of the 



DOUBLE-ACTING CONDENSING ENGINE. 125 

lower part of the apparatus from the opposite side. The same 
letters apply to the same parts in these four several figures. 

In the engine before us, the steam reaches a part of the steam- 
pipe marked s, whence it flows into a space formed around the 
Cylinder by a cylindrical case called the Jacket. The use of 
this is to keep the Cylinder itself at an uniform temperature. 
All engines have not this additional part, and in this country in 
particular we never recollect to have seen it used. For it, 
a simple casing of wood is frequently substituted, which, being 
a bad conducter, has been supposed to be well adapted to pre- 
serve the heat of the cylinder. 

From what has been said in respect to the mode in which heat 
is carried off under certain circumstances, it will appear that 
both Jacket and wooden casing are liable to objections. In the 
air, but little heat is carried off in consequence of the conduct- 
ing power of the surface, and by far the greatest part of the loss 
is due to radiation. Now, of the metals, the rough blackened 
surface of cast iron is among the best radiators, and wood stands 
high in the general order of radiating power; and hence, in the 
first case, the steam will be cooled before it reaches its place of 
action ; and in the second, the temperature of the Cylinder will 
be more affected than if it had not been cased. The principles 
we have discussed would point out as a sure method of retain- 
ing the heat, to enclose the Cylinder in an air-tight cylindrical 
case of some bright metal, with a thin body of air between them. 
The confined air will convey but little heat to the casing, and 
that which is conveyed will radiate very slowly. 

80. In the engine before us, the steam passes from the jacket 
to the side-pipes, marked a a, through the opening marked b. 
The form and arrangement of these pipes depends upon the 
structure of the valves ; in this engine the valves are of that 
description called the Slide- Yalve. This was originally in- 
vented by Murray, of Leeds, but was compressed by him with- 
in a shorter space ; the valve before us, which occupies the 
whole side-pipe, is an improvement of Watt's. 

81. The side-pipe has the general figure of a half cylinder, 



126 DOUBLE-ACTING 

the plane face of which is turned towards the Cylinder of the 
engine, and is terminated at top by a square box. The steam en- 
ters this pipe by a channel b. that communicates with the jacket. 
In engines that have no jacket, the steam-pipe usually enters 
the side-pipe from behind it, about the middle of its height. 

Within this pipe is placed another, which exactly fills it at 
the upper and lower extremity, but which is made less in the 
middle, so that the steam, on entering the side-pipe, fills up the 
space between the two pipes. The inner pipe is moveable, 
and attached to a rod that passes through an air-tight collar in 
the square box, of which we have spoken, and by which it is 
drawn up and pushed down alternately, under the action of a 
mechanism that will be hereafter described. 

Between the Cylinder and the outer pipe are two channels, 
whose section is rectangular. One of these forms a communi- 
cation with the upper, the other with the lower part of the 
Cylinder. 

The length of the inner pipe is so adjusted that when that 
part, at one of its extremities, which just fills up the outer pipe, 
is opposite to the corresponding rectangular passage, the other 
rectangular passage shall be opposite to the space that we have 
described as left between the middle part of the inner and the 
outer pipe. Hence, steam will flow into the Cylinder from 
this space. In the plane surface of the part of the inner pipe 
that is applied to the first-named rectangular passage, there is 
a corresponding rectangular opening, by which the steam, 
from the adjacent side of the piston, will pass into the inner 
pipe, and thence by a passage marked o into the condenser n. In 
the position in which the engine is represented in the figure, 
the steam is flowing into the lower part of the Cylinder, and 
beneath the piston, while it is passing out at the opposite end, 
and through the inner pipe to the condenser. 

The inner pipe has a similar rectangular opening at its op- 
posite extremity ; when, by the action of the engine, the inner 
pipe changes its position, this opening adapts itself to the ad- 
jacent rectangular passage ; while the other communicates with 
the space between the two pipes, and thus the direction of the 
steam and the motion of the piston are reversed. 



CONDENSING ENGINE. 



127 



It will therefore be seen that there is a constant communication 
between the space contained between the two pipes and the boil- 
er, while the inner pipe has a constant communication with 
the condenser. A change in the position of the inner pipe 
brings the openings of the Cylinder alternately into communi- 
cation with the boiler, and condenser. 

It is obvious that this species of valve requires very perfect 
workmanship ; the plane surfaces of the outer and inner pipe 
must be ground in the most careful and exact manner, and the 



BiiTl ' 



128 DOUBLE-ACTING 

circular surfaces, where they come in contact, at the upper and 
lower extremities, must also be accurately fitted. 

The structure and use of this species of valve will be better 
understood by reference to the figures on the preceding page, in 
which it is represented in two different positions. In order to 
give more variety, we have taken a form different from that of 
the engine in PL III. in which the spindle enters the side-pipe 
from above, while in the figure, the spindle is applied beneath. 

This valve, being as long as the Cylinder, has been called the 
Long Slide-valve, in order to distinguish it from one acting upon 
the same principle, but which does not occupy so great a space, 
and which is called the Short Slide-valve. PL L Fig. 6, re- 
presents a section of a cylinder, and side-pipes adapted for the 
occupation of a valve of the latter description ; and we shall 
describe it more fully hereafter, in treating of the kind of en- 
gine to which it is most frequently adapted. 

The valve which is most frequently used in modern English 
engines is also of the sliding form, but is divided into two parts, 
the one corresponding to the upper, the other to the lower end 
of the cylinder. The slides are connected by a rod. This form 
is called the double D valve, and is placed, like the puppet valve 
we are about to describe, between two side-pipes, one of which 
communicates with the boiler, the other with the condenser. 

Sliding valves have the advantage, which is in many cases 
important, of opening gradually, and thus causing no sudden 
shock when the motion of the engine is changed ; and by a 
proper adjustment of the distances between the openings of the 
inner pipe, and of the apparatus by which it is driven, it may 
be made to cut off the steam before the motion of the piston is 
completed, and thus again render the change less sudden. On 
the other hand, the accuracy of workmanship it requires may 
not be always attainable, and its repair cannot be effected in 
situations remote from well-organized workshops. It is also to 
be stated, that when impure water is used, it has been found to 
wear rapidly and unequally ; and thus, after having been intro- 
duced in many of our steam-boats, it was laid aside, and an- 
other and more ancient species of valve restored. Of this we 
shall proceed to give a description. 



CONDENSING ENGINE. 129 

82. This species of valve, usually called the puppet valve, is 
represented on PI. II, Fig. 3. 

The side pipes are two in number, of which that marked 
A, is continually receiving steam from the boiler, through the 
steam pipe E, while that marked B is constantly conveying it to 
the condenser. These pipes are united by being both inserted 
at each end into the same cylindrical case, or box, of which 
there are consequently two, at C and D. These are called 
Steam Chests, and each of them is divided into three spaces by 
two diaphragms, having each an opening of the form of a trun- 
cated cone, whose least base is lowermost. These appertures 
are called nozzles, and are the seats of the valves ; to these 
nozzles, four solid frusta of cones, a, b, c, d, are accurately 
ground, and form the valves ; from the space between the two 
diaphragms in each box, is an opening that allows the steam to 
pass to and from the cylinder. 

It will be obvious, that when the two upper valves, a and 
c, in each box, are raised, steam must flow from the boiler into 
the Cylinder, and when the two lower of each set, b and d, are 
raised, it must flow from the cylinder to the condenser. Hence, 
it is necessary that they should reciprocate, the valves a and d 
opening when the valves b and c close, and vice versa. Hence, 
the two valves, a and d, are united, and made to open and shut 
at the same time ; as are the two valves b and c. It will be 
perceived by the drawing, that each valve has a cylindrical 
spindle or stem attached to it, and the four nozzles are in the 
same vertical line. The spindles of the two steam valves, a 
and c, are hollow, and admit the spindles of the two condensing 
valves, b and d, to pass through them. The purpose of this 
will be explained hereafter. In more ancient forms of the en- 
gine, the spindles were replaced by a short rack, into the teeth 
of which the teeth of a circular segment caught. The use of 
this form will also be stated hereafter. 

In some engines, the steam and condensing valves of each 
pair are placed obliquely, instead of being in the same vertical 
line. In this case each spindle is solid and has its separate steam- 
tight collar. 

The most perfect form of valve is that of Trevithick. The 

17 



130 



DOUBLE-ACTING 



slide valve, if tight, is attended with great friction, and the puppet 
valve is kept in its seat by a pressure of steam, which, on each 
square inch of its surface, is equal to that on a similar area of the 
piston of the engine, and this resistance is estimated at more than 
the friction of a slide valve. The valve of Trevithick has the 




form of a cylinder, on the upper end of which, at c c, is a conical 
ring, and a hollow cone is turned at b b, on its inner and lower 
surface. The first of these conical surfaces rests in a hollow 
frustum e e, the second upon a solid frustum d d. It will there- 
fore be seen that the resistance to the opening of the valve, is 
the pressure on a surface equal to the difference between the 
areas of the conical surfaces, c c and b b, instead of that upon a 
circle whose diameter is c c. The arrows show the directions 
in which the steam flows. 

The side pipes sometimes have, for the sake of ornament, 
the form of pillars, the entablature being extended above to 
cover the space left vacant by the side pipes. 



CONDENSING ENGINE. 131 

The old rule for the side of these nozzles was, to make their 
least diameter one-fifth, at least, of the diameter of the Cylinder ; 
but one-fourth of that diameter is now a more usual dimension. 
The passages into the boiler must have an equal area, as must 
the passages of the slide valve that has just been described. 

83. The Cylinder of a steam engine has the figure which is 
denoted by its name ; and, in order to avoid ambiguity, it has 
been and will always be distinguished by beginning it with a 
capital, in order to prevent its being confounded with such 
other parts as have also a cylindrical form. It is represented 
in the figures on Plate III, by the letter b. 

This vessel is, in all large engines, made of cast iron, cast 
with a core, and reamed out to the proper size. This operation 
requires great care, and should be done in a mill liable to no 
agitation, for much of the value of the engine will depend upon 
the interior being as truly a mathematical cylinder as the nature 
of materials will admit. Near the upper end of the Cylinder is 
cast a rectangular piece, in which is the passage h ; and at both 
ends are cast flaunches, to admit the fastening of its lid and bot- 
tom, by means of screw-bolts and nuts. In the engine on the 
plate, the lid is screwed to a flaunch on the jacket, and the 
flaunch of the Cylinder secured to the jacket by packing. 

84. The lid of the Cylinder is a circular plate, whose diame- 
ter is equal to that of the flaunch to which it is adapted. On 
its lower side, it is turned, so that a circular projection fits the 
inside of the Cylinder, barely leaving room for the packing. In 
the middle is an opening to admit the passage of the piston-rod, 
and around this opening:, on the upper side of the lid, is cast 
a cylindrical stuffing-box, to receive the packing, by which the 
rod is made to work steam-tight. In small engines the upper 
part of this stuffing-box is cut into the form of a female screw, 
to receive the screw that compresses the packing, and the head 
of the former is turned into the form of a cup, to contain oil. 
In larger engines the oil cup is connected with the lower part of 
the stuffing-box by screw-bolts and nuts. 



132 DOUBLE-ACTING 

85. The bottom plate of the Cylinder is of the same diame- 
ter with the top, and has a similar projection turned upon it, to 
fit the Cylinder. The lower steam passage passes through it, 
and is cast in one piece with it. In the engine before us, the 
flaunches of the Cylinder and the jacket are united to the bot- 
tom by the same set of screw-bolts and nuts. 

The length of the Cylinder must be as much more than the 
length of the stroke of the piston as is equal to the thickness 
of the latter, and, in addition, a small space to prevent the piston 
from striking. In the engine on Plate III, the diameter of the 
Cylinder is equal to half the length of the piston's stroke. 
This proportion is not a constant one, but is that sanctioned by 
the general practice of Watt. In the English steam-boats 
where the engine is placed beneath the deck, the stroke is ne- 
cessarily short, and power is gained by increasing the diameter 
of the Cylinder. 

We shall have occasion, in speaking of steam-boats, to treat 
of the proper length of stroke for engines intended to propel 
them. In those which are applied to manufactures, the propor- 
tion stated above is perhaps the best. 

86. The piston is still usually composed of two pieces of 
circular section, that are just so much smaller than the internal 
section of the Cylinder, as to move in it freely without touch- 
ing. The lower piece is firmly attached to the piston-rod, by 
making the lower end of this rod of the shape of a truncated 
cone, of which the lesser base is uppermost, and of the same 
size with the rod. A key is passed through the rod just above 
the piston, and unites them firmly. 

The two pieces of which the piston is composed are connected 
by screws, and have a semicircular groove cut, as it were, out of 
their united mass, forming a ring completely around them. 
This open ring is occupied by the packing. The packing is 
usually formed of hemp, moistened by an oleaginous substance. 
This packing is compressed, and made to apply itself closely to 
the sides to the Cylinder, by the screws which unite the two 
pieces of which the piston is composed. As the packing wears, 
the screws are turned, and thus the packing, being again com- 



CONDENSING ENGINE. 



133 



pressed, is forced out, and again applies itself to the cylinder. 
This arrangement may be better understood by the following 
figure, which represents a section of the Piston : a is the Piston- 
rod terminating in the truncated cone b ; c c screws to unite 
the two parts of the piston, d d and e e ; //section of the pack- 
ing. 




87. An ingenious mode of tightening the packing without 
taking off the lid of the cylinder, was invented by Woolf. The 
head of each of the screws is cut into the form of a toothed 
pinion, and the teeth of all these work in a wheel, having a 
free motion around the piston-rod. It is. therefore, evident that 
if one of the pinions be turned, not only will the screws attach- 
ed to it be made to act, but all the others will be equally driven 
forward. One of the screws has a square head, which caYi be 
reached by a key passed through an opening in the lid of the 
Cylinder, and which is usually closed by an air-tight cap ; it 
may thus be turned, by removing the cap, and all the others will 
be turned equally by the wheel and pinions. 

In the figure annexed a is the piston rod, b b the wheel fit- 
ted loose upon it, c, c, c, c, c, pinions forming the heads of the 
screws that compress the packing, d square head formed upon 
one of the screws, by adapting a key to which, the wheel b b 
is turned, through the intervention of the pinion to whose 
screw the key is applied ; the wheel b b turns the remaining 
pinions, and with them the compressing screws. 



134 DOUBLE-ACTING 




88. Metallic packing appears likely to supersede all others, 
and has already done so in many instances. The earliest at- 
tempt at a substitute of metal for hemp was made by Cart- 
wright. Two rings of metal, accurately ground to fit the 
cylinder, are interposed between the upper and lower parts of 
the piston. Each of these rings is cut into three parts, and 
they are placed upon each other in such a manner that the 
joints of the one ring fall half way between the joints of the 
other, in the same manner as the break-joint of masonry. 
Three springs are made to act upon each of these rings, one 
at each joint, and thus to press the two adjacent pieces out- 
wards. In this manner the springs carry the rings outwards, 
to replace any diminution by wear, and the breaking of the 
joints prevents any escape of steam through the apertures that 
are thus made in either of the rings. 

The annexed figure shows this arrangement, where a is the 
piston-rod. b, b, b springs that press against the joints c, c, c of 
one of the rings, which is here represented as formed by in- 
scribing an equilateral triangle in a circle, d, d, d are parts of 
the three pieces that form the second ring, whose joints fall 
at the points e, e, e, against which springs similar to b, b, b 
press. 



CONDENSING ENGINE. 

e 



135 




In applying a metallic piston, accuracy in the boring is ab- 
solutely essential, nor can they be introduced except when this 
part of the workmanship is of the best description. 

Another form of metallic packing, which is represented be- 
neath, has been used in locomotive engines. It is composed of 




136 DOUBLE-ACTING 

a screw-formed ring, compressed between the plates of the piston. 
The several convolutions of the screw are united by solder, un- 
til they are turned down to the proper dimensions. The sol- 
der is then melted off. 

The most perfect form of metallic packing is one in which 
the elastic force of the steam itself is used as the spring. The 
piston in this case is a single cylindric plate of cast iron. Two 
flat rings are turned out off its curved surface, leaving three 
flaunches. The upper and lower flaunches are pierced by a 
number of small holes, by which the steam tends to pass into 
the flat rings. These rings are occupied by a double com- 
pound ring of bell-metal, the pieces of which are so arranged 
as to break joint, and thus prevent the steam from passing them 
and the inner surface of the Cylinder. This packing has the 
great advantage that its friction is exactly proportioned to the 
tension of the steam by which the engine is worked ; while in 
all other methods, if the packing is compressed sufficiently to 
be tight at the highest tension to which it is subjected, the fric- 
tion is enormous at lower tensions. 

89. The Condenser is a vessel of a cylindric form. It is re- 
presented in Fig. 2, PI. III. by n. Through the top passes the 
pipe o, which conveys the steam from the valves of the engine. 
On the side is an aperture, to which is adapted the valve r, called 
the Injection-cock, the use of which is to admit a constant jet 
of cold water to condense the steam. The capacity of the con- 
denser, when the engine works with steam of the pressure of 
17^-lbs. per inch, is usually one-eighth part of the capacity of the 
Cylinder. Its several dimensions are therefore each one-half 
of the corresponding measure of the cylinder. But when 
steam of greater tension is used, the size has been increased 
to half the capacity of the cylinder, and both have equal 
diameters. 

The state of the vacuum in the condenser is ascertained by 
means of a vacuum guage. This is represented PL I. Fig. 
14. a a is an open vessel of mercury, b b a glass tube im- 
mersed at one end in the mercury, and communicating at the 
other with the condenser through the tube e. As the vacuum 



CONDENSING ENGINE. 137 

is formed in the condenser, the presure of the external air will 
force the mercury up the tube 6 b, and the difference between 
the height to which it rises, and that at which the mercury of 
the barometer stands at the time, marks the resistance the gas- 
eous matter, that cannot be withdrawn from the condenser, of- 
fers to the descent of the piston. 

The Condenser communicates with the Air-Pump by a ho- 
rizontal passage of a rectangular shape. In this passage is si- 
uated the Foot-valve t. This has usually the form of a shutter 
hanging by a hinge on its upper side, in a position slightly in- 
clined from the vertical, and closing by its own weight. The 
valve is fitted to its seat by grinding or filing. The condenser 
and air-pump are screwed down to a common base called the 
bed-plate. 

90. The Air-pump q is also a cylindrical vessel, almost 
identical in figure with the Cylinder. In the engine before us it 
has half the lineal dimensions of the cylinder, and consequently 
one-eighth of the capacity, or one just equal to that of the con- 
denser. The lid of the air-pump is similar to that of the Cylin- 
der, permitting the passage of the rod through a stuffing-box. 

91. The piston of the air-pump is packed in the same man- 
ner as that of the cylinder, but, unlike it, is not solid. It con- 
tains a valve, which is usually of that form called the butterfly 
valve. In this shape, the Piston-Rod is attached to a bar ex- 
tending across the piston in the direction of one of its diam- 
eters ; to this are adapted by hinges, in such a manner as to 
open upwards, two shutters that fill up the rest of the circular 
opening of the piston. These shutters, therefore, rise and fall 
together like wings, whence their name. The piston and its 
valves are usually called the Bucket of the Air-pump. From 
the dimensions we have stated above, it will be obvious that the 
stroke of the Bucket is just half that of the Piston of the Cylin- 
der. A plan and section of an air-pump bucket are represented 
on the following page. 



18 



138 



DOUBLE-ACTING 





92. On the side of the Air-pump, and near its top, is cast a 
rectangular passage, which is closed by a valve v, similar in 
form and structure to the foot-valve, and which is called the 
Deliver in g:-door or Clack-valve. 



93. Upon the rise of bucket of the Air-pump, the water of 
condensation is discharged by the delivering-door into a rectan- 
gular vessel of iron w, called the Hot-water Cistern. The Hot- 
water Pump, by which the water of condensation, or at least 
as much of it as is necessary for the supply, is carried to the 
boiler, is represented at x. It is a common pump, composed of 
a barrel and two valves. The water converted into steam is, 
as we have seen on page 116, nVsth part of the capacity of the 



CONDENSING ENGINE. 139 

Cylinder for each stroke of the piston ; the pump is made to 
furnish a greater quantity, or -§i^th part, in order that there 
may be no risk of a defect in the supply. 

As the water of condensation is much greater in quantity 
than this, being twenty-two times as much in weight as the 
steam that is employed, a large portion of the water must run 
to waste, which it does by a waste-pipe. 

The calculation of the size of the hot-water pump may be 
made as follows, viz. 

Divide the cubic contents of the cylinder in inches by 900, 
and this quotient by the length of the stroke of the pump, the 
quotient icill be the area in square inches, ichence by the usual 
geometric rule the area of the valves may be calculated. 

The stroke of the hot- water pump in the engine on PI. III. 
is one-third of that of the cylinder. 

94. The condenser and air-pump are immersed in a cistern 
of water, called the cold-water cistern. In some engines 
this is a basin in the ground, lined with masonry, laid in ce- 
ment. In steam-boats it is omitted altogether, and its want 
supplied by increasing the size of the condenser. In other en- 
gines again, it forms a cast-iron trough or basin, on the sides of 
which the whole of the apparatus is supported. In the engine 
represented on PI. III. this is the case, as will be obviousfrom 
the several views in which it is represented, a a being this 
trough. An engine thus supported, and which may therefore 
be placed upon any solid basis, entirely independent of walls or 
buildings, is called a portable engine, even when of the largest 
dimensions. 

95. From the cold-water cistern, a pipe passes into the con- 
denser. The use of this is to admit a jet of water, to condense 
the steam with greater rapidity, by bringing it in contact with 
a greater surface. The extremity of this pipe is sometimes co- 
vered by a nozzle, pierced with holes like that of a watering-pot. 
The quantity of injection water is regulated by a valve called 
the Injection-cock, which is to be seen in Fig. 2. 



140 DOUBLE-ACTING 

96. As the injection-cock is constantly drawing- water from 
this cistern, and as the water it contains is constantly abstract- 
ing heat from the condenser and air-pump, it requires a con- 
tant and regular supply, as well to keep it at a proper temper- 
ature, as to renew what is actually expended. For this purpose 
the cold-water pump y is provided. It, like the hot-water 
pump, is a common pump, communicating with a reservoir of 
fresh water. We have, upon page 116, stated the quantity of 
water that is needed to keep the water in this cistern at the pro- 
per temperature, whence the area may readily be calculated 
when the length of the stroke is known. The length of the 
stroke of the cold-water pump, in the engine before us, is the 
same as that of the air-pump, or half that of the Cylinder. 

Hall's condenser, which has recently been introduced, is com- 
posed of a series of tubes immersed in the cold water cistern. 
The condensation is effected by the steam coming in contact with 
the cold surfaces of the tubes, instead of being caused principally 
by injected water. The tubes are freed from the condensed steam 
by an air-pump of the same size and structure as that we have 
described, and this is of sufficient power to diminish the ten- 
sion of the remaining vapour below that which is due to the 
temperature of condensation. The vacuum guage, consequent- 
ly, which in the common condenser does not rise above 26 
inches, has been maintained for days together in Hall's Con- 
denser at 29,5. 

In the engines to which Hall's Condenser has hitherto been 
adapted, steam of a tension little greater than a single atmo- 
sphere has been used. The air-pump has, therefore, sufficient 
power to pump the condensed water directly into the boiler. 
This it would not be able to do without much expenditure of 
the force of the engine, were steam of 2 or 3 atmospheres used, 
as is frequently the case in our American condensing engines. 
But their ordinary force-pump working in a hot cistern, would 
answer the purpose. In the use of this condenser the exact 
quantity of water which has passed through the engine in the 
form of steam is returned to the boiler at each stroke of the 
pump, and being obtained by the condensation of vapour, has 
the purity of distilled water. If, therefore, a boiler be filled at 



CONDENSING ENGINE. 141 

first with pure water, no inconvenience can possibly arise from 
the accumulation of solid matter. Nay, even sea-water may 
be used without its becoming - more injurious than at first. As 
there will be a waste arising from the escape of steam through 
the safety valves, a small distilling apparatus is added to the 
ordinary boilers ; so that no other water than what is obtained 
by condensation need be admitted into the boiler. It is 
obvious that this condenser is not only convenient, and capable 
of adding to the power of a given engine, but must be condu- 
cive to the safety of boilers in which there can be no deficiency 
of water as long as the engine remains in action. 

97. The theory and use of the Parallel Motion, 1, 2, 3. 4, 
has already been explained— see pages 116, 117. The rule 
for one of its most usual forms is as follows, viz : The 
parallel bar is half the length of one arm of the working beam, 
or one-fourth of the distance between the two glands. The 
radius-bar is of the same length with the parallel-bar. The two 
pairs of straps are, of course, equal in length, and are usually 
three inches less between their centres than the length of the 
half stroke of the piston-rod. 

The centre, to which the air-pump is attached, is in the in- 
ner pair of straps, at the point where a line drawn from the ful- 
crum of the lever beam, to the upper end of the piston-rod, cuts 
the inner strap. See page 106. 

98. The length of the lever-beam, in Watt's engines, is 
usually one and a half times the length of the stroke of the pis- 
ton-rod. The beam is usually cast in one piece. The centres 
of the parallel motion, pump rods, and connecting rod are 
turned out of rods of steel, and passed through the beam. In 
many modern engines the lever beam is a trussed frame of cast- 
iron, bound by a band of wrought-iron, and this is a most 
important improvement in the structure of the engine. 

99. The air-pump rod u being attached to the inner pair of 
straps, is at a distance, from the centre of motion of the lever- 
baem, of one-fourth of the length of the latter. 



142 DOUBLE-ACTING 

The rod of the cold-water pump is attached to the lever- 
beam, at an equal distance from the fulcrum on the opposite 
side. 

The rod of the hot- water pump is at a distance, from the ful- 
crum, of one-sixth of the length of the working-beam. 

The length of the connecting rod between the centres, in 
Watt's engines, is twice the length of the stroke of the piston. 
In most American engines it is three times that length ; and 
less is lost by obliquity of action in the latter case. 

100. The arm of the crank z, is half the length of the stroke 
of the piston in all cases where the arms of the lever-beam are 
of equal length. 

101. The radius of the Fly- Wheel may be various, accord- 
ing to the uses to which it is applied ; the motion for driving 
machinery ought to be taken off at a distance from its centre, 
equal to that of its centre of gyration. See page 7. In the 
engine on PI. III., the fly-wheel has a radius equal to twice 
the whole length of the cylinder. The weight is calculated 
by the following rule : 

Multiply the number of horse's powers of the engine by 
2000, and divide by the square of the velocity of the circum- 
ference of the wheel per second, the quotient is the weight in 
cwts. 

The velocity of the circumference is readily found when 
the radius is given, for the crank has a velocity as much great- 
er than that of the piston-rod as the circumference of a circle is 
greater than its diameter ; and the circumference of the fly- 
wheel has a velocity as much greater than the crank as the 
radius of the former is greater than that of the latter. 

In the first form of Watt's engines, the valves were opened 
and shut by apparatus of the same description with that which 
had been used in the more ancient forms. Tappets were at- 
tached to the rod of the air-pump, which, during the ascent and 
descent of the rod, acted upon levers with counterpoising 
weights. These levers were thus made to give a reciprocat- 
ing motion to toothed segments, that acted upon racks attach- 



CONDENSING ENGINE. 143 

ed to the valves, and thus opened and shut them. We shall 
return to this manner of working valves in the history of the 
engine. 

When conical valves are used, a spindle is attached to each, 
and the nozzles are immediately beneath each other. Thus 
the two spindles of each pair of valves are in the same vertical 
line ; the upper spindle in each pair is hollow, and the spindle 
of the lower valve passes through it. The weight of the valves 
is usually sufficient to close them, and keep them shut j if 
not, they are loaded until they shut themselves. In order to 
open them, the following arrangement is employed : — The 
spindles of the two valves, that are to act simultaneously, as, 
for instance, the steam valve of the upper pair and the condens- 
ing valve of the lower, are united by lifting rods, which have 
consequently the forms of three sides of a rectangle. These 
rods are pressed upwards at a particular part of the motion of 
the engine by pieces projecting from a horizontal shaft that 
has an oscillating motion. These projecting pieces or arms 
lie in the same plane, and on opposite sides of the shaft ; so that 
when one of them acts upon the rod that moves one pair of 
valves, and presses them upwards, the other ceases to act, and 
permits the other two to fall into their seats by their own weight. 
The return of this oscillating shaft permits the first pair of 
valves to shut, and causes the other piece, or cam, to act upon 
the two that were before shut. 

102. This oscillating shaft is called the Tumbling Shaft. It 
receives its motion by means of a small crank that is attached to 
it, and moves upon it as an axis. This crank is connected with 
the axle of the fly-wheel by an apparatus called the Eccentric. 
This is represented in Figs. 1 and 2, on PI. III., and is shown 
separately in Fig. 4. 

A circular plate b has an opening of a circular shape cast in 
it, but having an eccentric position in respect to it. This last 
circle just fits the shaft of the fly-wheel, and is wedged firmly 
to it, so that the latter carries the circular plate b around with 
it in its revolutions. 

To the circular plate is fitted a circular ring c, within which 



144 DOUBLE-ACTING 

it can turn, and which, therefore, need not receive any motion 
from it, but what arises from the eccentricity of the revolution 
of the plate. To this ring are attached two bars d, e, forming 
the sides of an isosceles triangle. These are united by frame- 
work. These bars terminate in a single piece, in the direction 
of a perpendicular to the base of a triangle, and which has a 
handle/ turned upon its extremity. The use of this handle is 
to lift the eccentric from its place, when it is wished to stop the 
engine, and return it again, when the engine is to be set in mo- 
tion. A notch of a semicircular figure is cut in the eccentric, 
which drops upon a pivot, turned upon the crank of the tum- 
ling shaft g. 

It will be obvious, that while the axis of the fly-wheel is car- 
ried around, and with it the circular plate, the end of the tri- 
angular frame will have an oscillating motion communicated to 
it, which the free motion of the ring e, will allow to be convert- 
ed into a reciprocating circular motion in the crank of the tum- 
bling shaft ; it will thus give the latter a motion suited to 
the opening of the valves, by means of the two arms that have 
been described. 

The engine upon the plate (PI. III.) has, as has been des- 
cribed, a slide valve. This is set in motion in a manner differ- 
ent from the puppet valves. 

An arm, h, projects from each end of the tumbling shaft, 
and both are in one plane at right angles to its crank, g, f. 
To these arms are attached two light lifting rods, that rise 
above the side-pipe where they are united by a cross head. 
To the middle of this is attached the rod that moves the slide, 
and thus the latter is both raised and depressed by the action of 
the eccentric, while as we have seen, the puppet valves are 
raised only, and return to their seats by their own weight. 

103. When an engine is used for purposes that occasionally 
require its motion to be reversed, two eccentrics may be employ- 
ed, that adapt themselves to cranks situated at the opposite ends of 
tumbling-shaft, in planes at right angles to each other. Only 
one of these eccentrics is used at a time ; when it is necessary 
to reverse the motion of the engine, the piston is stopped at 



CONDENSING ENGINE. 145 

half-stroke, or in the position represented in Figs. 1 and 2, on 
PI. III. The eccentrics are then exchanged ; that before in use 
being raised, and the notch of the other dropped upon its crank. 
When the steam again flows, the piston will return in a direc- 
tion opposite to that in which it was proceeding when stopped. 
Another method that has been used in some English steam- 
boats, consists in cutting two notches opposite to each other in 
the rod of the eccentric ; the rectangular cranks of the tumbling- 
shaft are at the same end of the shaft ; the eccentric lies between 
them, and may be made to apply itself to either at pleasure. 
This arrangement has also been so modified as to be placed 
within the control of the helmsman of a steam-boat. The ne- 
cessity of communicating with the engineer by conventional 
signals is thus avoided. 

104. It will be obvious that the time at which the valves 
open and shut may be determined by the position of the eccen- 
tric upon the shaft of the fly-wheel. This may be done, by 
this apparatus, far better than it can be by tappets upon the rod 
of the air-pump, or, as they are usually called, a plug-frame, 
This determination is of no small importance to the working of 
an engine. Should the piston be impelled by the steam to the 
very end of its stroke, a violent blow will take place between it 
and the head or bottom of the Cylinder ; while, on the other 
hand, if the steam-valves be opened too soon, a part of it will be 
expended in diminishing the action of the steam on the oppo- 
site side of the piston. In both cases power will be wasted, and 
the lost power will be exerted to injure the apparatus. In put- 
ting up an engine, the position of the eccentric is determined by 
actual trial, and the eccentric is left in the position where it is 
found to tend most to the equable and regular working of the 
engine. 

105. A band passing over a drum on the axis of the fly- 
wheel turns a second drum, which is upon the axis of a bevel 
wheel. This bevel wheel gives a motion to another, that car- 
ries upon its axis the Governor. This arrangement is repre- 
sented upon the plate, but could not be distinguished by letters. 

19 



146 DOUBLE-ACTING 

This governor, as has been stated, is a conical pendulum. The 
weights revolve in the same plane, which is raised by their 
centrifugal force when the velocity increases, and falls as the 
velocity of rotation diminishes. The theory of this instrument 
shows that its revolutions are half the number that would be 
performed by a pendulum, the length of which is equal to the 
distance of the plane in which the centres of the balls revolve, 
from the point where the bars, by which they are suspended, 
cross each other. Thus, then, if the least and greatest number 
of the revolutions that it is intended that the fly-wheel shall 
perform, in a given time, be known, it will be easy to calculate 
the length of the conical pendulum. 

106. The rods that bear the balls of the governor are united 
by pivots to two others, also connected by pivots, and sliding at 
their point of union upon the axis of the governor. The pa- 
rallelogram that is thus formed, is sometimes above the joint 
whence the balls hang, as in the horizontal engine on Plate 
VI, and sometimes below it, as in the high pressure engine on 
Plate V, or the separate figure of the governor on Plate IV, 
Fig. 2. In either case it gives motion to a lever, which acts 
at its opposite end upon a rod that moves the handle or lever 
of the throttle valve. This system of levers is so arranged that 
the throttle valve is opened to its utmost limit, when the balls 
of the governor are in their lowest position, and is wholly clos- 
ed, when they have been thrown out to their greatest extent by 
the centrifugal force. In the first case, therefore, all the steam 
that is generated, flows to the engine ; in the last, it is wholly 
cut off. 

107. The form of double-acting condensing engine which 
we have thus described, is that which is most commonly used 
in manufactures, particularly in Europe. It cannot, however, 
fail to have been remarked that it contains, at least, one part by 
no means necessary to its action : this is, the lever beam. The 
engine, as we shall see hereafter, was originally applied to the 
single action of pumping water, and in this the pump-rod, or 
brake, was conceived to be essential ; this, when made with 



CONDENSING ENGINE. 147 

equal arms, became the lever beam. Successive advances to- 
wards perfection in the structure were made, as improvements 
on the original plan, and not as original inventions. It has thus 
happened that an unnecessary and cumbrous part of the appa- 
ratus has been perpetuated. A far more simple form of the 
engine, and which is in many cases preferable, is that which 
was used by Fulton in his steam-boats, and of which one is 
represented on Plate VII It will be at once seen by inspec- 
tion, that in this engine the beam is suppressed, together with 
the parallel motion. Asa substitute for these parts, a cross-head 
a is adapted to the upper extremity of the piston-rod, b ; this 
works between vertical guides, a, a ; it is connected to the two 
cranks, c, c, by the two connecting rods, b 6, b 6, and to these is 
joined, in the case before us, the axis of the water wheels, d d ; 
the axis of the fly-wheel might in like manner be turned by 
these cranks, were it intended to apply the engine to general 
purposes. 

The pumps are worked by a beam, e e, far lighter than it 
need be in the other form of the engine, and but half the length. 
It is forked at the end nearest the cylinder, which it thus embra- 
ces, and is connected with the cross-head A of the piston-rod B, 
by the connecting rods, d d. 

The peculiarities in this engine, which adapt it to a steam-boat, 
will be described in another place. 

108. When a steam-engine is to be set in motion, the boiler 
must first be filled with water by hand, the fire lighted, and the 
steam raised to the proper tension. The steam and side-pipes, 
the Cylinder, eondenser, and air-pump, will be full of air, and 
the whole will be cold. The air must be extracted, and the en- 
gine heated up to the temperature corresponding to the tension 
of the steam, before it can be set to work. This is done by 
what is technically called blowing through the engine. All 
the valves are opened simultaneously by hand, and steam is 
thus introduced to all the parts. As steam is lighter than air, it 
will force the air from the cylinder towards the condenser. 
Hence the air is sometimes allowed to escape by a valve 
contrived for the purpose ; this is usually adapted to the con- 



148 DOUBLE-ACTING CONDENSING ENGINE. 

denser, by means of a pipe forming an elbow, and bent verti- 
cally upwards. This pipe is closed by a conical valve opening 
upwards. So long as air remains in the condenser, and is com- 
pressd by the steam from above, it is capable of making its way 
through this valve. The completion of the operation is shown 
by its being followed by steam, which, when this valve is situ- 
ated beneath the level of the water in the cold water cistern, is 
known by a slight crackling noise. It is, however, more usual 
in this country to suppress the valve on the side of the con- 
denser, or snifting-valve ; in this case the air makes its way 
through the air-pump, and is discharged at the clack-valve. 
When the steam thus shows itself, the injection cock is opened, 
a condensation of the steam in the condenser takes place almost 
instantly, and the pressure of the steam from the boiler becomes 
in a short time sufficient to put the engine in motion. The ec- 
centric is now applied to the crank of the tumbling shaft, and 
the engine becomes self-acting. 

In engines with slide valves, a simultaneous communica- 
tion cannot be made between the boiler and the two sides of 
the piston. An additional valve is therefore provided, making 
a communication between the lower end of the side pipe and 
the boiler. This is called the Blow-valve. It is opened by 
hand, and closed as soon as the engine is ready to work. This 
valve is to be seen on PI. III. 

To set a large engine in action has hitherto been a very la- 
borious operation, whether the slide or puppet valve be used. 
This difficulty was noticed by Trevithick, who contrived a dou- 
ble-seated valve, which required much less labour to work it. 
The most perfect construction of this kind is that brought into 
use by Mr. Adam Hall of New- York. In this the valves are 
so nicely balanced that a single man is able to blow through 
the most powerful engine. 



CHAPTER VI. 



GENERAL VIEW OP CONDENSING ENGINES ACTING EXPAN- 
SIVELY, OP HIGH. PRESSURE, SINGLE-ACTING, AND ATMOS- 
PHERIC ENGINES, PARTICULAR DESCRIPTION OP HIGH 
PRESSURE ENGINES. 

Regulation of steam by the valves of Condensing Engines. 
— Expansive force of steam, sujoposing the temperature to 
remain constant. — Expansive force of steam of a given 
tension, and in a given engine, on the same hypothesis. — 
Expansive action of steam of a given tension and constant 
temperature, when the friction and resistance is taken into 
view. — Expansive action at increasing tensions, and with 
temperatures varying according to the law of specific heat. 
— Effects of steam acting expansively, as usually employ- 
ed. — Action of high pressure steam when not condensed. — 
Cases in which high pressure engines are useful. — Recon- 
sideration of the precautions to be used in boilers generat- 
ing high steam. — General view of the high pressure en- 
gine, its steam pipes, side pipes, and valves. — Calculation 
of the power of high pressure engines, their ivorking beam, 
parallel motion, throttle-valve, governor, and forcing pump. 
— General view of the single-acting condensing atmosphe- 
ric engines. — Particular description of a high pressure en- 
gine, with a beam, and of long and short slide valves.— 
Particular description of a horizontal high pressure en- 
gine. — Description of a rotary engine. 

109. To set the Double Condensing Engine into motion, 
two of its valves must be opened. One of these admits steam 



150 CONDENSING ENGINES 

from the boiler, to act upon one side of the piston, while the 
other lets the steam from the opposite side pass into the con- 
denser. These two valves are united so as to open and shut 
together, as are the two which, alternating with them, give mo- 
tion to the piston in the opposite direction. These valves re- 
quire a certain space of time to open to their full extent, and 
thus the motion of the piston in the first instance, and the 
change at each successive alternation, are effected gradually. 
So aiso the valves are permitted to close before the engine has 
reached the limits of its stroke, and thus the shock the engine 
would sustain, and the consequent loss of power, are in some 
measure obviated. 

This may, obviously, be effected still more certainly, by cut- 
ting off the steam at an earlier period of the motion of the pis- 
ton, while the communication with the condenser is still left 
open. 

110. When the steam is cut off, it does not lose its whole 
power, nor does it lessen suddenly in force ; for, being elastic, 
and acting against a partial vacuum in the condenser, it will 
expand, until it either fill the Cylinder, or until the friction 
and the resistance of the partial vacuum in the condenser, be- 
come equivalent to its own expansive force. Watt, to whom 
we owe the double-condensing engine, was the first to remark 
that advantage might be taken of this to increase the effect of 
a given quantity of steam. Thus, if the Cylinder be but par- 
tially filled, and the steam then cut off, it will still act expan- 
sively, and all the force that it continues to exert is so much 
gained. Were the decrease of the temperature, arising from 
the change in the relation of the steam to specific heat, left out 
of view, the force of the expanding steam would decrease in a 
geometric progression, and might be calculated by means of ta- 
bles of hyperbolic logarithms. 

Calculated in this way, the power of a given quantity of 
steam would be increased in the ratios given on next page. 



ACTING EXPANSIVELY. 151 

Cylinder filled. Power of Steam. 

Wholly - .... l. 

One-half 1.69 

One-third - - - - 2.10 

One-fourth 2.39 

One-fifth - 2.61 

One- sixth - .' . - - - 2.79 

One-seventh - - - - 2.95 

One-eighth 3.08 

111. The advantages of using the Steam expansively would, 
therefore, according to this hypothesis, be very remarkable ; 
but to obtain them would require an entire remodelling of the 
engine and the alteration of its proportions. To use the same 
quantity of steam, it would be necessary that the steam 
pipes, the nozzles, and the Cylinder itself, should all be increas- 
ed in the ratio which the part of the Cylinder filled bears to 
the whole. If these remain unchanged, the consumption of 
steam, (supposing the temperature to remain constant,) would 
be lessened in the same ratio inverted, and the force with 
which the steam would act upon the piston, would have the 
following ratio : 

Cylinder filled. 

Wholly .... 
One-half ... 

One-third .... 

One-fourth - 

One-fifth - 

One-sixth ... 

One-seventh 

One-eighth ... 

These calculations are, as has been stated, made upon the hy- 
pothesis, that the temperature continues invariable, which is 
far from being the case ; for steam, like all other substances, 
has its capacity for specific heat increased during its expan- 
sion, and its temperature and consequent elasticity are dimin- 
ished. 



Force. 

1.00 


Steam expended. 
1 


0.84 


X 

2 


0.70 


JL 
3 


0.57 


X 
4 


0.52 


X 
5 


0.46 


X 
6 


0.42 


X 
7 


0.39 


X 

R 



152 CONDENSING ENGINES 

112. It must next be taken into view, that the absolute power 
of the steam is not all exerted ; for steam, as has been seen, act- 
ing with an expansive force of 17£ lbs. per square inch, is only- 
capable of overcoming a resistance equivalent to lOlbs. Hence, 
in an engine working at low pressure, the advantage gained by 
making it act expansively, would cease if the steam were cut 
off earlier than that at half the stroke, for at -^ the resistan- 
ces would be equal to the expansive force, even if the tempera- 
ture remained constant, which, as we have seen, it does not. 
The motion might, indeed, be kept up for a time by the fly- 
wheel ; but even then, without taking into view the irregulari- 
ties that would ensue, the effective action would diminish most 
rapidly, as will appear from the following calculated results : 

Cylinder filled with steam Mean effective Force, 

of 17 l-21bs. 

Wholly 1.00 

One-half 0.72 

One-third - 0.48 

One-fourth ----- 0.26 

ODe-fifth 0.17 

One-sixth - - - - - 0.06 

One-seventh - .' - 0.00 

We therefore conceive ourselves warranted in the conclusion, 
that when an engine acts expansively, the steam should never 
be permitted to expand itself to more than twice the bulk it oc- 
cupies under the atmospheric pressure. 

Working at low pressure, in order to produce an equal effect, 
the engine should be nearly one-half larger in its capacity, and 
the expense of fuel would be three-fourths of what it would be 
if the steam were employed in the usual manner. Unless, 
therefore, in cases where fuel is extremely scarce, there is pro- 
bably no real advantage to be gained in making low pressure 
steam act expansively. 

113. There is another point of view in which the expansive 
action of steam may be investigated, for the steam may be used 
at an increased pressure. If it have an expansive force of an 



ACTING EXPANSIVELY. 153 

atmosphere and a half, it would, if cut off at one-third of the 
stroke, expand, in filling the Cylinder, to the assumed limit of 
pressure, of half an atmosphere. The original effective force, 
after allowing for resistance, would be 151bs. per square inch, 
and the mean action would be two-thirds of that amount, or 
lOlbs. per inch during the whole stroke. Hence the engine 
would now work up to its nominal power. 

Steam, under a pressure of 1£ atmospheres, has, if we leave 
out of View the temperature, a density one and a half times as 
great as under atmospheric pressure simply ; hence, to fill one- 
third of the Cylinder would require the evaporation of as much 
water as would fill half the cylinder with steam of 212°. An en- 
gine, therefore, acting expansively with steam of the elasticity of 
H atmospheres, would, on this hypothesis, do the same work as 
when acting in the common manner, and consume but half 
the quantity of fuel. For, as the sum of the latent and sensible 
heat is the same, both in high and low steam, the quantity of water 
converted into steam is the same, whatever be its temperature. 

Let us next suppose the steam to have an elastic force equal 
to two atmospheres. It might, on the same hypothesis, expand 
to four times its original bulk before its elasticity became less 
than half an atmosphere. Hence it might be cut off at one- 
fourth of the stroke. 

Its original effective force, after deducting the constant resist- 
ance, will be 22^ lbs. per square inch, and it will act with a 
mean force of ffa of that amount, or upwards of 12^1bs. 
Hence the engine will, under such circumstances, work with 
one-fourth more than the power at which it would be estimat- 
ed according to the common rule. 

The steam would in this case also fill half the cylinder be- 
fore it reached the density of steam of 212°, and hence the 
quantity of water used, and fuel expended, would be the same 
as in the former. And, in all cases where the limit of the 
expansion of the steam is an elasticity equal to half an atmos- 
phere, the quantity of water evaporated and fuel expended 
would be constant. But the effective power would go on in- 
creasing with the elasticity of the steam, according to the fol- 
lowing table: 

20 



154 



CONDENSING ENGINE 



Relative power of the same engine acting in the ordinary 
manner, or expansively. The temperature being svpposed 
not to vary on expansion. 



-nl 



Steam in 


Cylinder 


Atmospheres. 


filled. 


n 


wholly 


1JL 


JL 


X 2 


3 


«> 


X 




4 


n 


JL 

5 


3 


6 


H 


JL 
7 


4 


J- 
8 



Fuel 
Expended. 



1 

0.5 
0.5 
0.5 
0.5 
0.5 
0.5 



Effective 
Force. 



10 
10 
12* 
15£ 

18 
19 
20 



114. In order to cut off the steam, a valve of the figure of a 
throttle valve is placed in the steam pipe. A weight, or strong 
spring closes it and keeps it shut, except when the one is lifted, 
or the other forced back, by the action of the engine. This is 
usually performed by placing two teeth or cams, of proper 
form and size, upon the axis of the crank. A plan of this kind 
may be seen on PI. IV. Fig. 4. where cis the axis of the crank, 
a and b two cams, or teeth, that act upon the spring g d, which 
is connected with the handle cfof the expansion valve, by the 
rod d e. F is a portion of the steam pipe. 

A very ingenious and simple mode of working a cut-off valve 
has been invented by Perkins, and applied to his expensive en- 
gine. He places an additional eccentric upon the shaft of his 
fly-wheel, to this is attached a jointed rod directed by guides. 
The end of this rod acts upon the lever of the valve, and by the 
adjustment of the length of the rod it may be made to act for a 
longer or shorter time. When the rod ceases to press the valve, 
a strong spring applied to it causes it to close. 

An addition has been made to the short slide valve, by which 
the steam may be cut off at any part of the stroke of the en- 
gine. 

A valve of the usual form is surrounded by a frame com- 
posed of two plates, each of sufficient surface to cover the 



ACTING EXPANSIVELY. 155 

steam passages. These plates are united by bars, which are 
pressed down by two strong springs. 

The eccentric is made to act upon a rod passing through a 
collar in an axle. To this collar it is adjusted by a screw in 
such a manner that the two arms of the rod may be made at 
pleasure to have different relations to each other. The space 
through which the eccentric moves one end of the rod being 
constant, the opposite end may be made to pass through differ- 
ent spaces according to the position of the point in the rod, 
which is made by the screw the axis of motion. It will there- 
fore be easily seen that the valve may in its motion be either 
made to strike the frame or not, at pleasure. In the latter case 
the steam will not be cut off, and by varying the motion in the 
former case, it may be cut off at any required point in the mo- 
tion of the piston. 

115. The estimate that has been given of the powers of steam 
acting expansively, is, as has been seen, formed upon the hypo- 
thesis that it expands to bulks that are inversely as the pressures. 
This is not the case, in consequence of the change of tempera- 
ture that the very act of expansion produces. Thus, the steam 
of a tension equivalent to half an atmosphere, has a tempera- 
ture of 180° and a density of 0.00032 ; while, with a tension of 
2, 3, and 4 atmospheres, it has the following densities : 



2 Atmospheres - 


0,00111 


3 do. .... . 


0.00160 


4 do. - 


0.00210 


earn of 




2 Amospheres expanding to 4 times its bulk, has 




a density of 


0.00028 


3 do. to 6 times its bulk, - 


0.00027 


4 do. to 8 times its bulk, - 


0.00026 



In a vessel which would neither give nor abstract heat, the 
tension and temperatures would be diminished, in the three 
several cases, in the ratios of f f or f , f f , and ff or f f . But in 
an expansive engine, the cylinder may be readily kept up to the 
temperature of the steam before it begins to expand, and the 



156 



CONDENSING ENGINE 



steam in expanding will derive heat from it. The method, 
which is occasionlly adopted in a low pressure engine, of enclo- 
sing the cylinder in an outer case, called a jacket, will be far 
more beneficial in an engine acting expansively, and the dimi- 
nution in tension, arising from diminished density, will be 
counteracted by increased heat. This, however, will be attend- 
ed with a loss of heat in the surrounding steam, and will require 
the capacity of the boiler to be increased in proportion. It is, 
therefore, to be taken into view, that the comparison of engines 
acting expansively, as given on page 154, is not absolutely true ; 
but that, in order to make it so, the fire surface of the boiler 
should be increased ^th at the pressure of two atmospheres, and 
£th at the pressure of four, and the safety valve loaded with ad- 
ditional weight in the same proportion. The expenditure of 
fuel will also be increased in the same degree. The advanta- 
ges derived from making engines act expansively are still great, 
notwithstanding this increase in the expenditure of fuel; for an 
engine receiving steam of the tension of 4.f atmospheres, cut 
off at £th of the stroke, will do twice as much work as one re- 
ceiving low steam, with but six-tenths of the fuel it expends. 
If we correct our previous calculations upon these principles, 
the results will be as follows, which will give the actual effect 
which may be produced by the same engine, acting at low pres- 
sure or expansively, with different loads on the safety valve. 

Relative 'powers of the same engine acting at loio pressure or 
expansively, the change in the relations of the expanding 
steam to temperature being taken into account. 



Load on the 
Safety Valve. 


Cylinder 
filled. 


Fuel 
Expended. 


Effective 
Force. 


31bs. 
lOlbs. 


wholly 
X 


1 

0.55 


10 
10 


19lbs. 


JL 


0.56 


12^ 


27lbs. 


X 


0.57 


15i 


36lbs. 


X 


0.58 


18 


46lbs. 


X 


0.59 


19 


571bs. 


X 
8 


0.60 


20 



*J 



ACTING EXPANSIVELY. 157 

This table is, however, far from exhibiting the whole advan- 
tage of which the method of cutting oif the steam before it has 
filled the cylinder is capable. It will be easily seen that our 
calculations would be only adapted to the case of a diminu- 
tion in the fire surface of the boiler, and that in practice a dif- 
ferent course would, be pursued ; — the same quantity of water 
would still continue to be evaporated, and the same amount of 
fuel expended, unless the whole system were changed. Let us 
then suppose that with a given engine and boiler, the steam is 
cut off at different portions of the stroke. If cut off at half 
stroke, the density of the steam will be doubled ; and if at one 
third, tripled, and so on. The tension of the steam will be in- 
creased even in a higher ratio, for steam of two atmospheres has 
a density of no more than 0.00110, while twice the density of 
steam of the tension of a single atmosphere is 0.00118. The 
usual pressure in the condensing engine also exceeds an atmos- 
phere by one-sixth, and the tension obtained by cutting off 
will be a multiple of this instead of one of a single atmosphere. 
We shall, however, neglect this in our view of the comparative 
effects of an engine working expansively,*with steam of different 
tensions. 

Relative poivers of an engine using the same quantity of 
fuel, and acting expansively at different tensions. 



force in Atmospheres. 






Cylinder filled 








Effective fore 


H - 


- 


- 


wholly 


- 


- 


- 


10 


2 


- 


- 




- 


- 


- 


10.75 


3 


- 


- 


i 


- 


• 


- 


27.5 


4 


- 


- 


4 


n 


. 


. 


35.6 


5 


- 


. 


5 


- 


- 


- 


43.5 


6 


- 


- 


X 
6 


- 


- 


- 


51. 



It will therefore appear that, without any change in the ge- 
neral distribution and plan of an engine, provided the boiler be 
strong enough to bear the increased force of the steam, its pow- 
er may be readily increased five-fold. This will be done with- 
out using steam of a temperature higher than is frequently 
employed in engines of a different structure. 



158 CONDENSING ENGINE 

It is more usual to cut off the steam at half stroke, and to de- 
pend, for an increase of force, upon an increased capacity of 
the boiler to generate steam. This method is, however, disad- 
vantageous, as it will require an alteration in the boiler, other 
than an increase of its strength ; and will, besides, demand a 
more powerful apparatus, and larger supply of cold water for 
keeping up the vacuum of the condenser. Nor does it give re- 
sults near as satisfactory as the mode to which we have just re- 
ferred, if the expenditure of fuel be taken into account, as will 
be perceived from the following table : 

Relative force of steam used expansively in a cylinder 
of constant dimensions, and always cut off at half-stroke. 

Force in atmospheres. 
2 
3 
4 
5 
6 

116. It may therefore be inferred, that the best mode of using 
the double acting condensing-engine, is to make it of the usual 
form and dimensions, and give it a boiler of sufficient strength, 
with a fire surface of the usual extent ; but to cut off the steam 
at as early a period of the stroke as may be considered safe. 
This method has been brought to the test of actual experiment 
in the pumping engines employed in the mines of Cornwall, 
and by its use, the power of an engine of a certain nominal 
horse power has been increased five-fold. 

The method of cutting off at half-stroke has been more es- 
pecially used in the steam-boats of this country, and the tension 
of the steam has been raised by increasing the fire surface of 
the boiler. The last object has been effected by a variety of 
artifices. It may, however, be fairly inferred, that the method 
of cutting off at such part of the stroke as corresponds to the 
desired increase in the tension of the steam is much preferable. 

High as our estimate of the advantages of using steam expan- 
sively may appear, it is, notwithstanding, far less than those of 



Fuel expended. 




Effective force. 


Force with the same fuel. 


- 1 


- 


- 


18.75 


- 


18.75 


- H 


- 


- 


32 - 


- 


21.67 


. 2 


- 


- 


45 - 


- 


22.5 


- H 


- 


- 


53 - 


. 


23 


- 3 


. 


. 


72 - 


« 


24 



ACTING EXPANSIVELY. 159 

Watt and Woolf. The former hazarded the opinion that 
steam of 41bs. was capable of expanding itself to 4 times its 
bulk, and still retaining the tension of an atmosphere. Woolf 
seized this expression as the basis of his calculations, and inferred 
that steam of 5, 6, 7, 8, &c. lbs, was capable of expanding as many 
times as the unit of measure of the safety valve was loaded with 
pounds. These views are wholly erroneous, and are contrary 
to the physical and mechanical properties of steam. 

Our own reduced estimates are more to be relied upon, and offer 
sufficient inducements for the employ of the expansive action 
of steam. 

Our calculations in respect to the increase of power gained 
by expansive action have reference, as will be at once seen, to a 
constant velocity in the working point of the engine. It may, 
however, happen that the resistance is constant, or increases 
with the velocity only ; and that the increase in the power 
arising from expansive action, is applied to an increase in the 
velocity. Analogous advantages will be gained in this case, 
which is that of steam navigation. 

116 b. It will easily be seen, from what has been stated in 
relation to the expansive action of steam in the condensing 
engine, and from what we shall in relation to the increase 
obtained in the force by using steam of great elastic force in 
the high pressure engine, that a given engine may be made 
to work far beyond its nominal power. The horse power 
is, in either case, estimated from the area of the piston, the 
height and velocity of its stroke, and the pressure taken at the 
amount which has hitherto been most frequently used. Thus, 
in the condensing engine, the pressure is usually estimated, after 
the resistances are allowed for, at lOlbs. per square inch ; and 
in high pressure engines, at 401bs. 

In the former engines, by increasing the tension of the steam 
in the boiler, and cutting it off in such a manner as to allow it 
to act by its expansive force, we have seen that the force given 
by the combustion of a given quantity of fuel, may be increased 
more than three-fold, and the action of a given engine doubled. 
A still greater effect may be produced, by using steam of higher 
tension than such as, in its expansion, will diminish to the limit 



160 CONDENSING ENGINE 

we have assumed in Chap. VI. In addition then, to the esti- 
mate in horse powers, which has now become of no other use 
than a mode of describing the size of an engine, in contracts 
between the maker and purchaser, it has become customary to 
compare the work of engines with each other, by a mode of es- 
timate which is called their Duty. The mode in which the 
duty of a steam engine is estimated is in the numbers of pounds 
which can be raised 1 foot high by the combustion of a single 
bushel of coals. We have seen that this quantity of coal is ca- 
pable oi evaporating 12 cubic feet of water, and therefore of 
keeping an engine of twelve horsepower in action ior an hour. 
It ought, therefore, according to the estimate we have just made, 
raise to a height of 1 foot 

24000 X60 X 12=17,2800001bs. 
or upwards of seventeen millions of pounds. Watt and Boul- 
ton constructed an engine, whose duty reached as high as 19 
millions ; and it was said that their own engine at Soho, did 
work equivalent to a duty of 21,6000001bs. ; but, on an exami- 
nation, in legal form, of all the engines they had put up in Corn- 
wall, two years before the expiration of their patent, it was 
found that the average duty was no more than 17 millions, or 
in strict conformity with our estimate. Many of these engines 
acted expansively ; and one performed a duty of 27 millions, in 
spite of which the average fell to the limit we have stated. 
The expiration of Watts' patent left engineers free to make 
such improvments as experience or science might suggest. The 
expansive action of steam was the improvement which was prin- 
cipally relied upon ; and, in order to obtain from it the greatest 
practicable advantage, for the old boilers of Watt, such as are 
figured on PI. I. were gradually substituted cylindric boilers ca- 
pable of bearing steam of great tension. In this way the force 
of the steam has been gradually raised from little more than a 
single atmosphere to 10, and an intelligent Cornish engineer 
states that he has seen it raised as high as 20 or 30 atmospheres. 
In this way the average duty has been regularly on the increase, 
being in 1833, 19| millions ; in 1814, 20^- millions ; in 1815. 
the same ; in 1816, nearly 23 millions ; in 1817, 26^- millions ; 
in 1818, 25^- millions ; in 1819, 26| millions ; in 1820, 28f 



ACTING EXPANSIVELY. 161 

millions ; in 1825,32 millions; in 1828, 37 millions; in 1829 
41 millions ; in 1830, 43^ millions. During this time, single 
engines have performed far more than the average, and in the 
year 1835, one has reached a duty of 94 millions. 

117. When steam of high pressure is used to propel engines, 
it is frequently made to act without the aid of a condenser, and 
consequently in opposition to the whole pressure of an atmos- 
phere. 

The engine, in this case, becomes much more simple, inas- 
much as the condenser and air-pump may be dispensed with, 
as well as the cold and hot water pumps ; but for the latter is 
substituted a forcing pump to feed the boiler, and in most cases 
a common pump will be needed, to raise the supply. The 
cold water cistern, and the water for condensation are no longer 
necessary, and thus a very great weight may be saved, which 
in some cases is of great importance. 

In estimating the resistances which the action of the steam 
meets with, it is to be considered, that the imperfection of the 
vacuum of a condensing engine merges in the pressure of the 
atmosphere, in one where the steam is not condensed ; and that 
thus the resistances, which, in the former, were estimated at 
7^-lbs. per square inch, may be diminished, as well as by the 
power required to work the air and cold-water pumps. The 
resistances, other than the pressure of the atmosphere, need not 
therefore be taken at more than 5lbs. per square inch, which, 
added to the pressure of the atmosphere, makes a constant re- 
sistance to the action of the steam, in a high pressure engine of 
201bs. per square inch. Hence, steam of an expansive force of 
two atmospheres will work in a given cylinder with the same 
force that steam of 17|lbs. would work in a condensing engine. 
But steam under a pressure of two atmospheres has rather less 
than two-thirds of the density of steam of 17|lbs. per inch ; and 
hence it would require more than l£ times as much water 
to be evaporated in order to fill the cylinder, and If times as 
much fuel. In this case, therefore, there would be a loss of 
50 per cent, in using a high pressure engine. 

If the steam had a pressure of 2£ atmospheres, its effective 

21 



162 



HIGH PRESSURE ENGINES. 



force would be 17|lbs. per square inch, or would bear, to that 
in a low pressure condensing engine, the ratio of 7 to 4. But, 
to fill the Cylinder with steam of corresponding density, would 
require nearly twice as much fuel. 

At a pressure of three atmospheres the effective power of the 
steam becomes 251bs. per square inch, or bears to that of a low 
pressure engine the ratio of 5 : 2. To fill the cylinder with 
steam of this density, requires fuel in about the same ratio ; and 
hence, at this limit, the power of high and low pressure en- 
gines, consuming the same quantity of fuel, becomes nearly 
equal. 

With four atmospheres' of steam, the effective pressure be- 
comes 401bs., the consumption of fuel is about three to one ; 
and here the high pressure engine has an advantage in the ra- 
tio of four to three. 

At five atmospheres, the effective pressure is 551bs. per inch, 
the ratio of water evaporated or fuel consumed as 3fths to 1. 
Arranging these and similar calculations in a table, we have as 
follows : 

Effect of High Pressure Steam to work Engines. 



fim mmiuimm 



Pressure in 


Fuel in the 


Force in the 


Force with the 


Atmospheres. 


same Engine. 


same Engine. 


same Fuel. 


2 


H 


1 


0.75 


2i 


2 


1.75 


0.875 


3 


H 


2.5 


1.000 


4 


3 


4 


1.333 


5 


3f 


5.5 


1.46 


6 


H 


7 


1.55 


10 


7 


13 


1.86 


20 


14 


28 


2.00 


30 


20 


43 


2.15 


40 


26 


58 


2.23 



118. It thus appears that the useful effect of high pressure 
engines increases far more slowly than the increase of the elastic 
force of the steam. This arises from the fact, that the density 
of steam increases nearly as fast as the pressure under which it 



HIGH PRESSURE ENGINES. 163 

is generated. Did both increase in the same ratio, there would 
be nothing gained by the use of high steam. A high pressure 
engine is, therefore, far inferior in power to one in which the 
steam acts expansively, and is subsequently condensed ; as will 
appear from a comparison of the preceding table with that on 
page 154. 

There are, however, cases in which the high pressure en- 
gine is preferable to any other. Thus, when water is scarce, 
the high pressure engine dispenses with the use of that em- 
ployed in condensing the steam, which, as we have seen, is 22 
times as great as that which is evaporated from the boiler. 
The weight of the air-pump and condenser, of the cold and hot 
water cisterns, as well as of the water they contain, are all 
saved. Hence, where locomotion is important, as where steam 
is employed to propel carriages upon railways, high pressure 
engines can alone be used. These engines are also much sim- 
pier in their construction, being composed of fewer parts ; and 
they occupy far less room than condensing engines, whether 
the latter act expansively or not. 

Advantages similar to those obtained in the condensing en- 
gine may be obtained by permitting the steam to act expan- 
sively in the high pressure engine. The obstacle to be sur- 
mounted in this case, is the danger which may be feared, from 
increasing the tension of the steam to so a high degree as 
would be necessary to obtain important results. 

119. Whether an engine be constructed to receive the most 
important advantages from the expansion of the steam, or be a 
simple high pressure engine, in which the steam, after it has 
caused the piston to perform its motion, is permitted to escape 
into the open air, the boiler must be so constructed as to con- 
tain and generate steam of high elastic force. Common high 
pressure engines work usually with steam of from five to six 
atmospheres, and there is no doubt that expansive engines 
might be constructed in such a manner as to be worked advan- 
tageously with a little less than five atmospheres. The load 
of the safety valve is at this latter limit 571bs., while to contain 
steam of six atmospheres, requires a load of 751bs. per square 



164 HIGH PRESSURE ENGINES. 

inch. It remains to inquire, how far it may be consistent with 
safety to employ steam of such expansive force 1 The prin- 
ciples on which the strength of boilers depends, have been 
fully illustrated in Chapter III. From what has there been 
stated, it will appear that the cylinder is the best form for boilers, 
and that a boiler of this shape, and of small diameter, may be 
made to resist the regular pressure of far more than six atmos- 
pheres ; that by diminishing the diameter of the cylinder the 
strength is increased in the inverse ratio of the squares of the 
diameters ; and that by a reduction in this dimension, any re- 
quired strength may be obtained. The application of the Hy- 
drostatic press furnishes a proof, in the first instance, of the co- 
hesive force of the material and the joints, to resist any given 
pressure ; and the proof may be finally completed by subjecting 
the boiler to the action of steam of more elastic force than it is 
ever likely to be compelled to bear in practice. The steam- 
guage will enable the engineer to know that the pressure is 
kept below the desired limit, and the safety valve opens as soon 
as that limit is reached. In case of a deficiency in the supply 
of water, or obstruction in the feeding apparatus, a thermometer 
will show the increased heat that is the consequence, and plates of 
fusible metal will melt as soon as a safe limit of heat is passed. 
A self-acting feeding apparatus will generally furnish a regular 
supply, for the failure of which the last-mentioned apparatus 
affords a safeguard. Registers and dampers will allow the fire 
to be moderated, and almost extinguished, whenever it becomes 
necessary. Next, the tendency of solid matter to collect and 
be deposited on the bottom of the boiler, may be lessened by 
mixing vegetable feculse with the water ; but careful cleansing 
will be required, at proper intervals, to obviate all danger from 
this cause. If an engine must be in constant operation, it 
ought never to have less than two boilers, one of which can be 
employed while the other is under repair ; and in all cases of 
constant employment, there should be one boiler more than is 
necessary to supply the engine. If the work be of such a nature, 
that the persons employed about the engine may have a tempta- 
tion to increase the force of the steam beyond the proper de- 



HIGH PRESSURE ENGINES. 165 

gree, there should be two safety valves, one of which should 
be beyond their control. 

No one of these precautions should be omitted when high 
steam is used, unless they are impossible from circumstances. 
In locomotive engines, and in steam-boats, spare boilers cannot 
be introduced ; the necessity for them, may, however, be done 
away, by prescribing stated periods of inactivity, when the boil- 
ers may be cleansed. 

With proper precautions, we do not hesitate to say that boilers 
in which steam is generated of no greater tension than is ne- 
cessary for giving the condensing engine its full power by ex- 
pansive action, may be rendered as little liable to accident as low 
pressure boilers ; and, indeed, the more common cause of explo- 
sion, namely, the exposure of the metallic flues, or the sides of 
boilers, to the fire, when not covered with water, is as likely to 
affect low pressure boilers as high. Of the two fatal explosions 
that have occurred in the harbour of New- York, one was a cop- 
per boiler containing low, the other an iron one containing high 
steam. But although, with proper precautions, high pressure 
boilers may be rendered as little liable to burst as those planned 
for generating low steam ; the explosions of the former, when 
they do take place, are more likely to produce dangerous con- 
sequences than the latter. We have ourselves been in two 
instances in steam-boats when low pressure boilers have given 
way, and the fact was only known by the stopping of the en- 
gine. This will always be the case when they give way un- 
der the ordinary pressure of the steam, for, supposing the safety 
valve to be loaded with 31bs. per inch, the escape of no more 
than a fifth part of the steam will restore the equilibrium be- 
tween the outer and inner sides of the boiler. Even if the 
boiler burst at the limit of its proof, the quantity of steam that 
can escape is little more than the half of that it contains in it. 

In boilers containing steam of four or five atmospheres, a 
rent will allow the steam to expand itself to four or five times 
its original bulk, even when it takes place under ordinary cir- 
cumstances ; while if it occur at the limit of the proof, in con- 
sequence of the safety valve ceasing to act, the steam may have 
a tendency to expand itself to ten or twelve times its original 



166 HIGH PRESSURE ENGINES. 

bulk, and even in the former case the explosion may be dan- 
gerous. In a low pressure engine, then, any dangerous explo- 
sion that can occur, grows out of the subsidence of the water 
below its proper level, and the very weakness of its material is 
a cause of safety. While in a high pressure boiler, the same 
risk is incurred, and, in addition, a giving way, even under the 
usual state of the steam, may sometimes be dangerous. 

A boiler, however, that has been properly proved, and is ex- 
amined at regular stated periods, cannot well burst, except by 
the clogging of its safety valve, or by the uncovering of its sides 
and flues. The former accident may be considered as hardly 
within the limit of possibility, if theguages of the engine are in 
order, and the engineer attentive to his duty ; and as both species 
of boiler are equally liable to the latter, we conceive that it may 
be considered as certain that no more risk is now incurred by 
using high pressure steam than by using low. 

In expressing this opinion, it may be repeated that proper safe- 
ty apparatus must be applied to the high pressure boiler, and that 
in steam-boats and locomotive engines there should be an ad- 
ditional safety valve, beyond the control of any person on 
board the former, or entrusted with the management of the lat- 
ter. Moreover, the practice which is said to prevail on the 
Mississippi, of using steam of 10, 15, or even 25 atmospheres, is 
to be reprobated. 

120. Such being our views of the possibility of using high 
steam with safety, cylindrical boilers, generating high steam, 
are rapidly superseding all others. They are applied in most 
cases to condensing engines acting expansively ; but where sav- 
ing of weight or of room, and even of original cost, is an object ; 
in locomotive carriages ; in boats navigating shallow rivers ; 
and wherever water is scarce : high pressure engines will be 
employed. Being less complex, they will also be preferred 
wherever good workmen to perform the repairs, or intelligent 
engineers, are not to be obtained. Upon the laud, such boilers 
should be simple cylinders, having the fire-place and flue be- 
neath them. But in steam-boats and locomotive engines, inter- 
nal furnaces and flues are indispensable. 



HIGH PRESSURE ENGINES. 167 

121. The parts of a high pressure engine are the following : 
A steam-pipe through which the steam passes from the boiler ; 
the area of this is calculated upon the principles laid down on 
page 89. 

Side pipes connected at one extremity with the steam-pipe, 
and at the other with the open air. In these are situated the 
valves which admit steam alternately to the opposite sides of 
the piston, or permit its escape. The original form of the valve 
was a cock with two passages and four openings, proposed at 
first by Leupold, and adopted both by Trevithick and Evans. 
This valve is represented on the next page. M N is the 
cylinder of the engine ; a b the side-pipe, in the middle of which 
is a conical socket, to which is adapted a frustum of a cone, 
with two passages d e, and consequently four openings ; c is the 
steam pipe, and fg the exhaust-pipe, or in a condensing engine 
the communication with the condenser ; h is the lever by which 
the valve is turned through a quadrant at each stroke of the 
piston ; and i is the other position of the lever. The steam, in 
the position of the valve that is represented on the drawing, 
flows from the pipe c through the passage e into the lower part 
of the side pipe b, and thence enters beneath the piston ; while 
the steam above the piston flows out at a through the passage d 
into the pipe/g*; in the other position of the valve, the motion 
of the steam is obviously reversed. 



168 



HIGH PRESSURE ENGINES. 




For this, in almost all high pressure engines, has been substi- 
tuted a short slide valve, which has been found by experience 
to be more advantageous. This valve is worked by an Eccen- 
tric placed upon the axis of the crank; a convenient mode of 
doing this is represented upon PL IV. at Fig. 3, where, 

A is the axis of the crank ; 

B the circular plate, a a a a triangular frame ; 

b rod and adjusting screw ; 

c handle, d arm of tumbling shaft ; 

e axis of tumbling shaft ; 

ff spindle of slide valve ; 



HIGH PRESSURE ENGINES. 169 

g g steam chest ; 

H steam pipe ; 

I eduction, or exhaust pipe ; 

k k bottom of cylinder, on which is casta piece 1 1 containing 
one of the steam passages. 

A plan and section of this valve are represented on PL II. 
Fig. 5, and will be described hereafter. 

The Cylinder resembles in form that of a condensing engine, 
fitted with a piston, and piston-rod passing steam-tight, through 
the cover of the engine. 

122. The power of the engine is calculated by taking the 
continued product of : the effective pressure of the steam per 
square inch in lbs., the area of the piston, the length of stroke 
in feet, and the number of strokes per minute ; which product 
divided by 33000 gives the number of horse powers. The 
effective pressure of the steam is 201bs. less than its absolute 
expansive force, or 51bs. less per inch than the load of the safety 
valve. It is, however, usually calculated at two-thirds of the 
pressure of the steam, which is the true amount when the 
steam is equivalent to 4 atmospheres, or the safety valve is 
loaded with 451bs. per square inch. 

123. The action of the piston may be conveyed to the work- 
ing points of the engine in the same manner as in the condens- 
ing engine. All, therefore, that has been said on pages 104, 
et seq., is applicable here. So also, when the machinery 
requires regulation, a fly-wheel is adapted to the crank, and 
where the work must be performed at a constant velocity, a 
Governor, acting upon a throttle-valve, is adapted. 

A parallel motion for a high pressure engine is represented 
on PL IV. Fig. 1. In this, 

c d represents the lever-beam ; 

b the piston-rod ; 

c and d the pivots or centres of the parallel motion ; 

e the pivot to which the piston rod is attached ; 

g g a part of a fixed frame that bears the pivot h of the 
radius bar ; 

22 



170 ATMOSPHERIC ENGINE. 

c e and df&ve the straps ; 

hf the radius bar; 

e/the parallel bar. 

The governor of a high pressure engine is represented on 
the same plate at Fig. 2 ; a and b are the two bevel wheels ; 

c d the axis of the governor; 

e e spherical weights, suspended by rods from joints on a 
fixed collar/; 

g is a collar sliding on the axis c d, by the motion of the bars 
g K g h ; 

i i is a circular arc forming a loop at each end, in which the 
bars/ h, fh play; 

g h k is a lever moving on the pivot k ; 

1 1 a connecting rod that unites the end / of the lever to the 
handle or lever of the throttle valve. 

124. The forcing pump that feeds the boiler, and the lift- 
pump that supplies the water which the former injects, are 
worked by rods from the lever beam, when the engine has one. 
In other cases, motions are taken off from the piston-rod in 
guch a way as to answer the same purpose. 

125. The high pressure engine is thus fitted to subserve all 
the objects that can be fulfilled by the double-acting condensing 
engine. There are, however, engines which are not suited to 
produce more than a reciprocating action, and which were of 
older date, although of less value, being applicable to but few 
purposes. Such is the single-acting condensing engine. In 
this engine, the lever-beam is loaded with a weight, at the end 
opposite to that to which the piston is attached, and the latter 
rests, when the engine is not in action, at the top of the Cylin- 
der. The Cylinder and steam passages are then filled with 
steam ; a communication is now opened, from the lower side 
of the piston, with the condenser, and the pressure of the steam 
on the upper side forces the piston down to the bottom of the 
Cylinder ; the steam and condensing valves are next closed, 
and the third valve, which forms a communication between 
the opposite sides of the piston, is opened ; there being now no 



ATMOSPHERIC ENGINE. 171 

resistance to the motion of the piston, other than the friction, 
the weight at the opposite end of the beam again preponderates, 
and the piston is drawn back to its pristine position, the steam 
flowing through the open valve and steam pipe from the upper 
to the lower side of the piston. 

In this engine the steam acts only during the downward 
stroke of the piston, and during its return no force is exerted 
upon the piston. The effort is, therefore, directed to raise a 
weight, which may, in its descent, perform a work of such 
nature as is suited to this peculiar species of alternating motion. 
The raising of water, by a forcing pump, is the most usual 
purpose to which such an engine is applied. 

A parallel motion is unnecessary in this engine, and the 
piston-rod is connected with the beam by a chain, that applies 
itself to a circular arc on the end of the beam. The pump-rod, 
loaded with a weight, is attached in a similar manner to the 
opposite end of the beam. 

The air-pump, the cold and hot water pumps, are attached to 
rods worked by the beam. 

The power of this engine being exerted during one motion 
of the piston only, is obviously no more than half of that of a 
double-acting condensing engine of the same dimensions. It is, 
besides, applicable to but very few purposes : and as these very 
purposes may be accomplished by a double-acting condensing 
engine of half the size, this form has gradually fallen into disuse. 
It was, however, at one time much in use for draining the 
water of mines, and raising that fluid for the supply of cities ; 
and it has not wholly gone out of use for the former purpose, 
in its application to which its powers have been increased by 
making the steam act expansively. 

1 26. At a still earlier period in the history of the Steam En- 
gine, an engine was employed, in which the air of the atmos- 
phere acting upon the piston was the prime mover. The 
vacuum on the lower side of the piston is caused by a conden- 
sation, effected in the cylinder itself. This engine is, for the 
reasons mentioned on page 102, far inferior to those in which a 
separate condenser is employed. It is also inferior in effect to 



172 HIGH PRESSURE ENGINES. 

an engine in which steam is the moving power, for the latter is 
always made to act with a force a little superior to simple at- 
mospheric pressure. 

127. The form of engine last mentioned is now obsolete, 
and the preceding one nearly so. The expansive engine 
does not dhTer in form from the double-acting condensing en- 
gine : we shall therefore restrict ourselves to the description 
of the high pressure engine, and leave the detail of the others 
until we treat of the history of the invention. 

On PI. V. is represented a high pressure engine of 30 horse 
power, manufactured by the West Point Foundry Association. 

a is the cylinder, the stroke of whose piston is about three 
and a half times the diameter. It stands upon a rectangular 
vessel i, through which the waste steam passes, heating water 
that is raised to it by a lift pump, not represented in the plate. 

The piston-rod b, is seen only in the end view, and is hidden 
in the other by the sides c c, in which its cross-head moves. 
This rod is attached to a lever-beam d, by straps a a, whose 
length from centre to centre is half the stroke of the piston- 
rod. 

d is the lever-beam, the length of each of whose arms is ra- 
ther more than three times as much as the stroke of the engine. 

e the Connecting-rod or Shackle-bar. 

f the Crank. 

g g, the Fly-wheel. 

h, a reservoir of water, through which the waste steam passes 
by a pipe, until it finally escapes by the tube r r. 

f f, is the eccentric, which moves the tumbling shaft k, to 
which is attached, by connecting rods, a cross-head I, which 
gives motion to the slide valve contained in the side pipe b. 

g g, is an endless chain passing over drums, one on the axis 
of the crank, the other on that of the vertical bevel-wheel. 

h, are two bevel-wheels that give motion to the axis of the 
governor k. 

While the balls of ihe governor diverge, they raise one end 
of the lever i, the opposite end is pressed down and closes the 
throttle valve, situated at c, in the steam-pipe. 



HIGH PRESSURE ENGINES. 173 

d is the rod of the forcing pump that conveys water from the 
reservoir h, to the boiler. 

A section of the Cylinder of this engine, and of its slide valve, 
is represented on PI. II. Fig. 4. 

fj lower passage for the steam. 

e, upper passage for do. 

h l f openings in the sliding pipe, adapting themselves alter- 
nately to the passages e and/. 

g, third opening in the steam pipe, represented as applying 
itself to the eduction passage m. 

m, eduction passage to which the openings I and g apply 
themselves alternately. 

i, i, interior of the side pipe, in which the slide is worked 
by the spindle. 

k, spindle, connected by rods with the eccentric. 

Another slide valve for a high pressure engine is represented 
in its connexion with the Cylinder at Fig. 5, on the same 
plate. 

a, b, c, d, is a rectangular bar of cast-iron, called the steam- 
chest ; it is constantly receiving steam from the boiler. The 
lower side of this has three openings, represented at g, c,f, in 
the ground plan. 

Within the steam-chest, is a septum g, being a cup, or trough 
of a rectangular shape, whose open face is downwards, and is 
ground to apply itself closely to the lower plate of the steam- 
chest, against which it is firmly pressed by the steam. 

This septum is of such a size as to cover two of the openings 
of the plate, and to exclude the third. Hence, one or other 
of the lateral openings always communicates with the middle 
opening, through the septum, while the remaining one receives 
steam from the steam-chest. This septum is drawn backwards 
and forwards by the spindle h, which is worked by an eccentric. 

The central opening c, corresponds to the eduction pipe by 
which steam escapes ; the other two communicate, one with the 
upper part of the Cylinder, the other with the lower, and in the 
varying positions of the sliding septum, steam is alternately 
admitted from the steam-chest, and allowed to escape by the 
eduction pipe through these apertures. 



174 HIGH PRESSURE ENGINES. 

A Horizontal high pressure Engine, manufactured by the 
West Point Foundry, is shewn on PI. VI., together with its two 
cylindrical boilers. 

A, ashpit. 

B, B, furnace doors. 

C, C, boilers. 

D, cylinder. 

E, piston-rod. 

F, connecting rod. 

G, G, G, fly wheel. 
H, governor. 

I, reservoir of cold water. 

K, forcing pump. 

L, cistern of water to be heated by waste steam. 

a, pipe forming communication between the water in the two 
boilers. 

b, 6, 6, steam pipe. 

c, safety valve. 

d, lever and weight of safety valve. 

e, pipe for waste steam from safety valve. 

/, pipe for waste steam after it has passed the valves and been 
used in the cylinders. 

g, steam chest containing slide valve. 

h, pipe by which the cold water is conveyed to the reservoir I. 

i, pipe by which water passes from the reservoir to the cold 
water cistern. 

k, continuation of pipe /. 

I, I, I, parallel motion for vertical forcing pump. 

n, n, n, eccentric. 

o, tumbling shaft. 

A section of the cylinder of this engine, with its side pipe, is 
to be found on PI. II. Fig. 6th. 

It has been objected to the horizontal form of Steam Engines, 
that the packing wears unequally, being first abraded on the 
lower side of the piston, and that the Cylinder itself must final- 
ly be worn into an elliptical shape. With proper precautions 
in the use, however, no practical difficulty need arise. Engines 
of this form have advantage, in various cases, that will hereaf- 



HIGH PRESSURE ENGINES. 175 

ter be enumerated, particularly in their application to steam- 
boats. 

High pressure engines are also occasionally constructed 
without the lever beam ; the form and distribution of the parts 
resemble, in this case, the condensing engine figured on PI. VII. 

In consequence of the loss arising in the conversion of the 
reciprocating rectilinear motion of the piston of the usual forms 
of steam engines into one which is circular, by means of the 
crank, a loss which is supposed by many persons to be much 
greater than it really is, it has been frequently attempted to ob- 
tain a rotary motion directly. For this purpose a very great 
number of engines have been planned, and many of them have 
been constructed and actually tested. In four of them have the 
views of the projectors been realized ; nay, it might at one time 
have been safely stated that all attempts at the construction of 
a rotary engine had resulted in failure. From this general 
censure might perhaps be excepted the engine of James. Still, 
its action has not been found to be as efficient as that of the more 
usual forms of engine, using the same quantity of fuel. At the 
present moment, however, (1836,) an engine in which a rotary 
motion is produced by the reaction of steam, is in the course of 
experiment, and there is great reason to hope that it will be 
successful. It has been tried in several instances with such 
results as to make it certain that as great a power can be ob- 
tained from it in many cases by a given quantity of fuel than 
in any other mode in which steam has been applied. Practical 
difficulties exist in applying it to all the various objects for 
which the steam engine is used, particularly when it may be 
necessary to change the direction of the motion. This engine 
is the invention of — Avery, of Syracuse, N. Y. 



CHAPTER "VIL 

EARLY HISTORY OF THE STEAM ENGINE. 

Introduction. — Statue of Memnon. — Hero of Alexandria. — 
Eolvpyle. — Anthemius and Zeno. — Cardan. — Mathesius. 
— Baptista de Porta. — De Causs. — Brancas. — Wilkins 
and Kircher. — Marquis of Worcester. — Hautefeuille. — 
Papirfs first plan. — ISavary. — Papin's Engine for the 
Elector of Hesse. — Newcomen and Cawley. — Potter's Scog- 
gan. — BeightorCs Hand- Gear. — Smeaton. — Leupold. 

128. The description of the steam engine, given in the pre- 
vious chapters, has been limited to the three more important 
varieties : the double-acting condensing engine impelled by low 
steam ; the double engine acting expansively ; the high pres- 
sure engine. These alone are in general actual use, and the 
consideration of their theory is all that is directly valuable to the 
maker or user of steam engines. The various other forms 
that the engine has assumed, in its progress from rude begin- 
nings to its present improved state, the several projects that 
have been brought forward and successively abandoned, may 
be best treated of in the historical form. In this manner also, 
may the relative merit of the inventors and improvers be best 
set forth. 

The steam engine, as it is the most powerful agent by which 
the power of man has been extended, so also has it employed 
the labour, ingenuity, and talent of more individuals than any 
other human invention. 

To give the true history of the steam engine, as indeed of 



HISTORY OF THE STEAM ENGINE. 177 

most of the discoveries which have conferred important benefits 
on mankind, would be, in fact, to enter into the annals of near- 
ly all the arts and sciences. Instruments have been frequently 
contrived, and principles stated, for which the world was not 
at the time prepared. Centuries sometimes elapse before the 
period arrives at which the wants of society call for their appli- 
cation, or the intelligence of the age can appreciate their merit. 
Then some more fortunate genius recalls the forgotten plan 
from oblivion, or, unconcious of the labours of his predeces- 
sors, derives from his own resources, inventions, not perhaps 
more meritorious than theirs in the abstract, but suited to the 
condition and wants of his cotemporaries. To the last then 
is the World really indebted, and to him is the gratitude due. 
His predecessors may have even gone beyond him in actual 
progress, his cotemporaries may have been upon the eve of the 
same discovery, and may have been so far advanced, that a few 
years, months, or even days, would have placed them by his 
side. But the good fortune, and it may perhaps be little 
more, of him who first reaches the useful result, must eclipse 
the merit of all others. Priority in the application of an inven- 
tion to practical purposes, if associated with originality, or even 
with the calling up of forgotten projects, that were impractica- 
ble or useless at the moment of their first conception, is the point 
on which a claim to high distinction in the annals of the useful 
arts must depend. 

In the history of the steam engine then, a few names stand 
prominent, in consequence of the immediate advantages to the 
world with which their labours were followed. Savary, who 
first successfully substituted steam for the labour of animals ; 
Newcomen, who first succeeded in applying it to move a solid 
body, through whose intervention the work might be perform- 
ed ; Watt, who called in physical science, to discover and reme- 
dy the defects of his predecessors, and made the steam-engine 
an instrument of universal application ; Fulton, who performed 
the first successful voyage by the impulse of steam ; and Evans 
and Trevithick, who cotemporaneously gave to the engine such 
a form as suited it for locomotion on land, and ascertained that 
such locomotion was practicable. 

23 



178 HISTORY OF THE STEAM ENGINE. 

It is necessary, before we enter into the history, to particular- 
ize these authors of the great steps the steam engine has made, 
in principle or in application ; for the more minute our inqui- 
ries become, the more will the real and vastly superior merit 
of these parties seem to descend to the level of others, whose 
ingenuity either formed the basis of the strides made by those 
we have named ; who had previously nearly reached the same 
results ; or were on the very eve of attaining them. Thus 
Savary and Newcomen, united, did but little more than the 
Marquis of Worcester had done before them, but had not ap- 
plied to purposes of real utility ; Watt found a competitor in the 
person of Gainsborough ; and but a few weeks would have plac- 
ed Stevens on the very eminence where Fulton now stands. 

The fitness of the time at which these several inventors suc- 
ceeded in their projects, if it be rather to be ascribed to good 
fortune than to pre-eminent merit, tends still more than any other 
cause to separate them from their competitors. Had the mines 
of Cornwall been still wrought near the surface, Savary or New- 
comen would hardly have found a vent for their engines. Had 
the manufactures of England been wanting in labour-saving 
machinery, the double-acting engine of Watt would have been 
suited to no useful application ; a very few years earlier than 
the voyage of Fulton, the Hudson could not have furnished 
trade or travel to support a steam-boat, and the Mississippi was 
in possession of dispersed hordes of savages. 

But if good fortune in the circumstances of the time, or in 
the success of the enterprize, were to be arguments against the 
honours that history assigns, we should sink its greatest names 
to the level of the most obscure, and those who have changed 
the face of the earth, to those who prepared, by gradual steps, 
the means by which the changes were effected. In the history 
of a mechanical invention too, it may frequently appear, on a 
cursory examination, that those who, by unsuccessful, although 
ingenious efforts, actually retarded the progress of discovery, 
are as meritorious as those who convinced the world of the 
value and practical merit of their inventions. So soon, how- 
ever, as success is attained, jealousy calls up all analogous pro- 
jects, however far from being adapted to the times at which 



HERO OF ALEXANDRIA. 179 

they were proposed, or which some simple but undiscovered 
step prevented from being introduced into practice, and ranges 
them on an equal level with, or even exalts them beyond, those 
to whom the world owes the perfected invention. 

Conflicting national pride too comes in aid of individual jea- 
lousy, and the writers of one nation often. claim for their own 
vain and inefficient projectors the honours due to the success- 
ful enterprize of a foreigner. 

If success be a title to honour in general history, it ought to be 
still more so in mechanical inventions. They require, to bring 
them into use, an union of practical and theoretic attainments, 
the want of either of which may render them abortive. Few 
projectors are thus doubly qualified, at the commencement of 
their career ; and few or none have been successful, until by 
long and costly experience, they have added practice to theoretic 
knowledge, or have, by laborious study, brought science to the 
aid of mere mechanical skill. 

That steam is capable of exerting a mechanical force must 
have been obvious from the most remote antiquity, for we have 
no reason to believe that man was ever ignorant of the use of 
fire. But to apply steam to any useful purpose is an idea com- 
paratively recent. Still, however, the remotest antiquity that 
can be reached by profane history, has been quoted as affording 
an instance of the employment of steam, if not for a useful pur- 
pose, at least for one that produced no unimportant effect at 
the time, and excited the curiosity of mankind for centuries. 

129. The elder Hero of Alexandria, who lived about 130 years 
before the Christian era, is the first author who gives any ac- 
count of the application of the vapour of water. We are una- 
ble to quote his work in the original, but are indebted for a no- 
tice of it to the beautiful little treatise of Stuart, to which we, 
once for all, acknowledge our obligations.* In this work it is 
stated that Hero expressly ascribes the sounds produced by 
the statue of Memnon to steam generated in the pedestal, and 

* Historical and Descriptive Anecdotes of Steam-Engines, and of their Inven- 
tors and Improvements, by Robert Stuart, Civil Engineer. — London, 1829. 



180 



HERO OF ALEXANDRIA. 



issuing from its mouth. Now, by the researches of Champol- 
lion, who is the highest authority on this point, the Memnon 
of the Greeks is identified with Amenophis II., a prince of the 
17th Egyptian dynasty, who reigned at Thebes 1600 years 
before Christ. Here, then, we have an application of steam, if 
the surmise of Hero be true, before the date of the Exodus of 
the Israelites, We must, however, express our opinion, that 
this is rather an ingenious explanation of the philosopher him- 
self of the mode in which he could have effected the same ob- 
ject, than an account of what was really performed by the 
Egyptian priests. 

130. Hero constructed or described more than one instru- 
ment, entitled to the epithet of steam engine. Two of them, 
of which one would have answered to raise water and the 
Other would have produced a rotary motion, are figured below. 




In the figure marked b, a is a vessel in which water is boil- 
ed ; the pipe c proceeds nearly to its bottom ; the steam will 
therefore accumulate in the upper part of the vessel, and force 
the water in a jet through the pipe c. A fountain may thus be 
formed, on which may be supported the ball o. 

In the figure marked c, o is a similar vessel ; two pipes, a 
and c, proceed from it ; these are bent towards each other, and 
serve as pivots to the sphere i, in which there are openings cor- 
responding to those in the pipes a and c. From points in the 



HERO. 181 

sphere diametrically opposite to each other, proceed the pipes m 
and ?i, which are bent towards the end at right angles, and direct- 
ed to opposite sides of the apparatus. The steam generated in 
the vessel o passes through the pipes a and c, into the sphere i, 
and thence into the pipes m and n, issuing from which in op- 
posite directions, it, by its reaction, gives a rotary motion to the 
sphere. 

Hero does not give the slighest hint that his invention was 
capable of any useful application, nor does he appear to have 
imagined that he was in possession of an instrument that was 
in future ages to produce such important results. 

The Greek philosophers, however, seem rarely to have at- 
tended to the practical value of their investigations ; it was suf- 
ficient for them to discover and to astonish ; and even when 
they mention arts and instruments that seem to have been ac- 
tually introduced, they avoid contemptuously all notice of their 
uses in the arts. " The ancient philosophers," says an ingenious 
author, " esteemed it an essential part of learning to conceal 
their knowledge from the uninitiated ; and a consequence of their 
opinion that its dignity was lessened by its being shared with 
common minds, was their considering the introduction of mecha- 
nical subjects into the regions of philosophy, as a degradation 
of its noble profession, insomuch that those very authors among 
them, who were the most eminent for their own inventions, and 
were willing by their own practice to manifest unto the world 
these artificial wonders, were, notwithstanding, so infected by 
this blind superstition, as not to leave any thing in writing 
concerning the grounds and matters of these operations ; by 
which means it is that posterity hath unhappily lost, not only 
the benefit of these particular discoveries, but also the proficient 
cy of these arts in general. For when once learned men did 
forbid the reducing them to vulgar use and vulgar experiment, 
others did thereupon refuse those studies as being but empty 
and idle speculations ; and the divine Plato would rather choose 
to deprive mankind of those useful and excellent inventions 
than expose the profession to the ignorant vulgar." We are 
luckily fallen upon happier times. The student and the profi- 
cient in science no longer shut themselves up from the busy 



182 EOLIPYLE. 

world, or hide their acquisitions like mysteries from the public ; 
but their whole endeavour is to bring their learning into such 
a form as may calculate it for the most wide dissemination, and 
enable it to produce the most extensive usefulness. 

132. The Eolipyle, however, was an instrument well known 
to the ancients. It was applied by them to but one single ob- 
ject, that of exciting the energy of combustion. It is mentioned 
by Vitruvius, Ltb. I. Cap. VI., as an illustration of the causes 
of the winds. It was supposed that the blast actually proceed- 
ed from the Eolipyle, but asjsteam would not support combus- 
tion, we must look to some other cause for its effects in this res- 
pect. We find it in the lateral communication of motion that 
takes place among fluids, by which a current of air is made to 
follow the course of the steam that issues from the neck of the 
Eolipyle. We give a figure of this instrument. 




It is composed of a globe or other hollow vessel A, to which 
a pipe B, is adapted. If a portion of water be introduced, and 
the vessel placed over a fire, steam will be generated, and issue 
forcibly from the narrow aperture. If it be mounted on wheels, 
it will recoil by the reaction of the escaping vapour ; and a ro- 
tary motion may be produced, by two pipes, but in opposite 
directions, as in the machine of Hero. 

133. A knowledge of some of the properties of steam seems 



CARDAN — BAPTISTA PORTA. 183 

to have been retained during the flourishing periods, and even 
to the decline, of the Roman empire. In the reign of Justinian 
a dispute occurred between Anthemius, the Architect of that 
Emperor, and the Orator Zeno, which shows this fact. Yet the 
knowledge was here applied to mere purposes of private malice, 
while it might, by the exercise of no greater ingenuity, have 
produced important and useful consequences. From this pe- 
riod until the revival of learning, we find no record of any use of 
steam, either for useful or entertaining purposes. 

134. Cardan is the earliest modern author in whom we de- 
tect any hint of a knowledge of the mechanical properties of 
steam. This extraordinary man, who united all the learning 
of his age to even more than all its superstition, appears to have 
known, not only the expansive force of steam, but the fact that 
a vacuum could be produced by its condensation ; a fact so im- 
portant in the action of the steam engine. Among his propo- 
sals is one for the use of the current of rarified air in a chim- 
ney, to produce a rotary motion. He, first of the moderns, 
gives a description of the Eolipyle. The work which contains 
the former of these plans is dated 1571.* 

135. A German of the name of Mathesius, in 1571, to bor- 
row the words of Stuart, " displayed almost as much ingenuity in 
contriving to introduce so untoward a subject into a sermon as a 
description of an apparatus, answering to a steam engine, as 
would be required to invent the machine itself, and which he 
gives as an illustration of what mighty efforts could be produc- 
ed by the volcanic force of a little imprisoned vapour." 

136. The researches of modern writers, among whom we 
may note with the highest praise him that we have just men- 
tioned, has disclosed various persons, who seem to have had 
ideas more or less just of the mechanical power of steam. The 
only one that we consider worthy of notice is Baptista Porta, a 
Neapolitan, who lived towards the close of the sixteenth centu- 

* Stuart's Historical Anecdotes of the Steam Engine, page 19. 



184 



DE CAUSS. 



ry. His machine, which is the germ of several that have been 
noted as original, is figured below, 




Water is boiled in a vessel A, placed upon a furnace. The 
steam rises through the pipe b into the upper part of the box or 
vessel C, the lower part of which is filled with water. The 
pressure of the steam on the surface of the water forces it up 
the rising pipe D. 



137. Next in the order of time is De Gauss, 
engines contrived by him is the following: 



Anions - various 




BRANCA S WORCESTER. 185 

A spherical vessel A has a pipe b b inserted, until it nearly 
reaches its lower part. The vessel is partly filled with water, 
which is boiled, and the steam accumulating in the upper part, 
forces the water up the pipe. Here it will be observed that the 
heated water is itself raised, and the powers and utility of the 
engine are evidently far less than those of the machine of Por- 
ta. 

138. The first person who seems to have had an idea that 
the power of steam was capable of being applied to any other 
useful purpose than that of raising water, was Brancas, an Ita- 
lian, who proposed to direct the blast issuing from an Eolipyle 
upon the leaves of a wheel, which, being set in motion by its 
impetus, might serve to move machinery. This method is un- 
luckily imperfect and wasteful, yet the attempt is deserving the 
highest praise, inasmuch as he is the only person, who, in the 
infancy of these investigations, entertained any hope of realiz- 
ing the vast benefits that steam has since conferred upon the 
world. Had steam been confined in its action to the single ob- 
ject of raising water, it might have been of notable use in a few 
cases ; but its great and important value, as a prime-mover, has 
been only realized since methods of applying it, to any species 
of work whatsoever, have been discovered. 

139. This plan of Brancas was repeated by Bishop Wilkins ; 
and Kircher proposed to apply two Eolipyles to concur in the 
same effect. The last-named author also proposed an engine 
similar in principle to that of Porta. 

140. Of all those who attempted to apply steam to useful pur- 
poses, without being successful in introducing his engine into 
general practice, the Marquis of Worcester fills the greatest 
space. He has been claimed by English authors as the first 
who made any experiments of importance upon steam ; and it 
has been asserted that the next of their countrymen, who un- 
dertook the investigation, did no more than copy, without ac- 
knowledgment, the plans of Worcester. Even the first truly 
successful form the steam engine assumed has been shown to be 

24 



186 WORCESTER. 

consistent, in many respects, with the description of one of the 
engines of this nobleman. 

It is yet a disputed point, what was actually the form of the 
engine of Worcester. His description is at best vague, and is 
without any figure ; various authors have exercised their inge- 
nuity in framing plans of a machine that should be consistent 
with the expressions of his work. "We do not consider it im- 
portant to do so, but shall content ourselves with quoting his 
own words. They are to be found in a little treatise, entitled 
" A century of the names and scantlings of such inventions, as 
at 'present I can call to mind to have tried and perfected, 
which, my former notes being lost, I have at the instance of a 
powerful friend endeavoured, now in the year 1655, to set 
down in such a way as may sufficiently instruct one to put 
the whole of them into practice." This work was originally 
printed in London in 1663, and has been six times reprinted ; 
the reprint of 1813 has been consulted for the following, being 
the 68th Proposition. 

" An admirable and most forcible way to drive up water by 
fire, not drawing or sucking it upwards, for that must be, as a 
philosopher calleth it, infra spheram activitatis, which is but 
at such distance, but this way hath no bounder, if the vessels 
be strong enough ; for I have taken a piece of a whole cannon, 
whereof the end was burst, and rilled it three quarters full, 
stopping and screwing up the broken end, as also the touch- 
hole, and making a constant fire under it ; within twenty-four 
hours it burst, and made a great crack ; so that, having found 
a way to make my vessels so that they are strengthened by the 
force within them, and the one to fill after the other, have seen 
the water to run like a constant fountain forty feet high ; one 
vessel of water, rarified by fire, driveth up forty of cold water ; 
and a man that attends the work is but to turn two cocks, that 
one vessel of water being consumed, another begins to force and 
refill with water, and so successively." 

Yague as this description is, it would still be possible to con- 
struct an engine that would perform a similar work by the ex- 
pansive force of steam. It would be very inferior to modern 
engines, but would yet be effectual. 



WORCESTER. 187 

It has generally been imagined that this is the sole reference 
to steam in the Century. But two others certainly correspond 
so closely to the character of our modern high pressure engines, 
that it may not be amiss to quote them also. They are the 
ninety-eighth and hundredth propositions of his work. 

" An engine so contrived that working primum mobile 
backward or forward, upward or downward, circularly or con- 
trariwise, to and fro, upright or downright, yet the pretended 
operation eontinueth and advanceth, none of the motions above 
mentioned hindering, much less stopping the other ; but unani- 
mously agreeing, they all augment and contribute strength to 
the intended work and operation ; and therefore I call this a 
semi-omnipotent engine, and do intend that a model thereof 
be buried with me." 

" How to make one pound weight to raise an hundred as 
high as one pound falleth, and yet the hundred pound descend- 
ing, doth what nothing less than one hundred pounds can effect. 
Upon so important a help as these two last-mentioned inven- 
tions, a waterwork is, by many years' experience and labour, so 
advantageously by me contrivedy.that a child's force bringeth up 
an hundred feet high, an incredible quantity of water, even two 
feet diameter, so naturally that the work will not be heard into 
the next room; and with so great ease and geometrical sym- 
metry, though it work day and night from one year's end to 
the other, it will not require forty shillings reparation to the 
whole engine, nor hinder one day's work ; and I may boldly 
call it the most stupendous work in the whole world ; and not 
only with little charge to drain all sorts of mines, and furnish 
cities with water, though never so high seated, as well as to 
keep them sweet, running through several streets, and so per- 
forming the work of scavengers, as well as furnishing the in- 
habitants with water enough for their private occasions ; but 
likewise supplying rivers with sufficient water to maintain and 
make them portable from town to town, and for bettering of 
lands all the way it runs. With many more advantageous and 
yet greater effects of profits, admiration, and consequence ; so 
that, deservedly, I deem this invention to crown my labours, to 



188 WORCESTER. 

reward my expenses, and make my thoughts acquiesce in the 
way of further inventions." 

In the first of these steam obviously meets the description of 
his primum mobile, for in whatever direction it proceeds, it is 
still capable of exerting the same mechanical force. The sin- 
gle pound raising one hundred, in the second, meets the con- 
ditions under which the piston of a steam engine acts, for its 
weight bears even a less proportion to the power of the engine. 

The following is an extract from a manuscript left by the 
Marquis of Worcester. 

" By this I can make a vessel of as great burthen as the ri- 
ver can bear to go against the stream. 

* # # ■ * # # # * * * 

" And this engine is applicable to any vessel or boat whatso- 
ever, without being therefore made on purpose ; and worketh 
these effects. It roweth, it draweth, it driveth, (if need be) to 
pass London Bridge, against the stream at low water." 

It is to be remarked, that Worcester claims, on his title-page, 
the merit of having actually completed, and used all the inven- 
tions he describes in the work : in support of this assertion va- 
rious evidence has recently been adduced. 

He employed a mechanic for thirty-five years, under his di- 
rections, in the manufacture of models ; and many of his projects 
that appear, in his manner of announcing them, absolutely im- 
possible, have been unexpectedly realized by modern inven- 
tions. 

That the steam engine of Worcester was no vague concep- 
tion, but was actually put into operation, a recent discovery 
has settled, upon testimony the most convincing. The Grand 
Duke of Tuscany, Cosmo de Medicis, travelled in England in 
1656. His manuscript account of his journey remained un- 
published until 1818, when a translation was made and printed. 
The following is an extract from this translation : 

" His highness, that he might not lose the day uselessly, went 
again after dinner to the other side of the city, extending his 
excursions as far as Yauxhall, beyond the palace of the Arch- 
bishop of Canterbury, to see an hydraulic machine, invented by 
my Lord Somerset, Marquis of Worcester. It raises water 



HAUTEFEUILLE MORLAND. 189 

more than forty geometrical feet by the power of one man only ; 
and in a very short space of time will draw up four vessels of 
water, through a tube or channel not more than a span in 
width." 

Here, then, is a description of an engine in actual operation, 
and corresponding in terms with that referred to in the century 
of inventions. 

141. In the several projects of which we have hitherto spo- 
ken, the expansive power of steam was used alone. It was 
made to act directly upon the surface of water to raise it; or, 
issuing from the orifice of an Eolipyle, set a wheel in motion ; 
or again, issuing from two tubes attached to an Eolipyle, caus- 
ed that instrument to revolve upon an axis, by the reaction of the 
vapour. In each of these ways the use of high steam is essen- 
tial to success, and this upon a large scale is attended with dan- 
ger, particularly in the low state of mechanic arts, and before 
the various contrivances we have mentioned in chapter III. 
were invented. 

The action of steam of a force no more than equal to the 
pressure of the atmosphere, against a vacuum formed by its 
own condensation, is a far more safe, and, as we have seen, 
more useful application of its energy. The researches of Stuart 
seem to show that this was first proposed by a Frenchman of 
the name of Hautefeuille. He, in the year 1678,* published 
a work, in which he intimates that the alternate generation 
and condensation of the vapour of alcohol might be applied, 
without waste, to the production of mechanical effects. We 
have, however, no proof that this project ever went farther 
than the mere proposal. It is, notwithstanding, to be consi- 
dered as one far beyond the knowledge of that age, of the nature 
and properties of steam. 

142. Sir Samuel Morland, who was cotemporary, appears, 
from the very words he employs, to have been merely an imita- 
tor of the Marquis of Worcester, and therefore claims no notice 
among those who aided in the progress of the steam-engine. 

* Stuart's " Anecdotes." 



190 MORLAND — PAPIN. 

143. In 1680, the year previous to that in which Sir S. 
Morland visited France, Dr. DenysPapin,a French Protestant, 
invented the safety valve, which has since been of such impor- 
tant service in the construction of the steam engine. It was 
first employed by him in an apparatus called the digester. This 
apparatus is a boiler, within which water is retained under 
pressure, in order that it may be heated beyond the tempera- 
ture at which it boils in the open air. The original object was 
to extract the gelatinous matter from bones, in order to apply 
its solution as food. To prevent any risk of danger, a conical 
aperture was left in the lid of the vessel, and to this was adapt- 
ed a conical stopper, pressed by a weight suspended at the end 
of a lever. It was, in short, identical with the most usual form 
of safety valves at the present day. 

Although he thus employed water at a high temperature, and 
had discovered one of the methods that are still in use, of ren- 
dering the boiler safe, still it was long before he attempted to 
apply the power of steam. The motion of a piston in a cylin- 
der was suggested by him, as a method of adapting the expan- 
sive force of an elastic fluid to produce mechanical effects. In 
this apparatus he at first proposed to employ air rarified by 
heat ; he next attempted to exhaust the space beneath the pis- 
ton, and make use of the pressure of the atmosphere ; and final- 
ly, to raise the piston by the inflammation of gunpowder. In 
a letter to Count Zinzendorf, however, he proposes to use steam 
for the same purposes. In the Leipzig Transactions, also, for 
the year 1690, he repeats the proposition, and explains the prin- 
ciple upon which he founds the application of this substance, 
both to raise a piston, and to produce a vacuum by its conden- 
sation. There is, however, no evidence that a separate boiler 
ever entered into his views, without which it would have been 
impossible to make any useful application of his principle. 

Nothing, then, had been actually effected by Papin in this 
earlier stage of his researches, and he did not extend them far- 
ther until steam had actually been successfully employed in 
raising water ; if we can indeed say that he ever was success- 
ful in pointing out a mode in which it could be rendered of 
practical value. 



SAVABT. 191 

144. The history of steam, applied to purposes of acknow- 
ledged utility, commences then with Savary. It has been 
much debated whether this person were in reality an inven- 
tor, or had merely the judgment to perceive an opening for 
the introduction and adaption of previous discoveries. His 
own statement is, however, clear, distinct, and worthy of cre- 
dit. Having been, in the early part of his life, employed in the 
mines of Cornwall, he was aware of the vast expenditure in- 
curred in keeping them free of water ; and an accidental obser- 
vation appeared to point out to him a simple and easy mode, 
in which a substitute could be found for the expensive labour 
of animals. Being at a tavern in London, he threw upon the 
fire a Florence flask containing a small quantity of wine ; he 
observed the wine to boil, and a cloud of vapour to issue from 
the neck, while the interior remained transparent. Struck 
with the appearance, he seized the flask and inverted the neck 
in a basin of water ; after a short time he found the flask filled 
with liquid, in consequence of the condensation of the steam 
forming a vacuum, into which the water was raised by the 
pressure of the atmosphere. 

The very form and arrangement of his apparatus is a proof 
of the truth of his story, for it is no more than a flask-shaped 
vessel of iron, in which a vacuum is formed by the conden- 
sation of steam. This part of its principle had not before 
been acted upon, nor even thought of, except in the suggestion 
of Hautefeuille, which we have before spoken of. The action 
of the vessel is in this respect identical in principle with that 
of the common pump. He did not, however, limit his viewsto 
this single action, but proceeded to add to it the action of the 
forcing-pump. For this purpose, so sopn as the flask was fill- 
ed with water, steam proceeding from the boiler, of a high tem- 
perature and corresponding tension, was admitted into the flask, 
after the communication with the water beneath was closed, 
which, acting on the surface of the water contained in the ves- 
sel, forced it up a lateral pipe. As it was impossible to obtain 
a perfect vacuum by the condensation of the steam, the first 
part of the action of Savary's engine was limited to the height 
of 25 feet ; the second part has no limit, but in the tension of the 



192 SAVARY. 

steam, and the strength of the materials, of which the vessel 
and the rising-pipe were composed. This however, was, from 
the imperfect state of materials and workmanship, limited to 
less than 70 feet ; so that the two different actions of the engine, 
working in succession, raised the water to little more than 90 
feet. Even at this comparatively small limit, the danger attend- 
ing the use of this engine became excessive, while the height, 
to which it was capable of raising water, was entirely too small 
for the purpose of draining mines. Several different engines, 
placed at different levels, would have remedied the last defect, but 
the cost of attendance would have been enhanced in proportion. 
Such defects were obvious ; there were, however, others which 
could not be accounted for until the doctrine of latent heat 
was discovered, and which we shall return to on a subsequent 
page. 

The cause which affects the action of high pressure engines, 
and prevents them from working with the power that might, at 
first sight, have been anticipated, is also to be found in opera- 
tion in this engine. The force required to raise water from 
sixty-five to seventy feet, is equivalent to steam of a tension 
of not less than three atmospheres ; now, as the density of steam 
increases nearly as rapidly as its tension, it is obvious that to 
obtain this in quantity sufficient to fill the vessel, would require 
the evaporation of nearly three times as much water as would 
fill it, were the tension no more than a single atmosphere. Hence, 
in fact, little is gained by the second part of the action of this 
engine ; for water may be raised, with an equal expenditure of 
fuel, nearly as high by condensation, in vessels placed at differ- 
ent levels, as it is by direct pressure of any intensity, however 
great. 

We have placed on the opposite page a section of the engine of 
Savary, which in its complete form was double, one vessel receiv- 
ing the water in consequence of the condensation of the steam, 
while from the other it was forced up by direct pressure; these 
vessels alternated with each other in their operation. 



SAVARY. 



193 




I is the boiler in which the steam is generated. 

O, steam pipe, by which steam is conveyed to the vessel P. 

q q, pipe communicating with a reservoir beneath ; through 
this pipe the water is raised to the vessel P, where the steam is 
condensed by the pressure of the atmosphere. 

S, rising-pipe through which water is forced when the steam 
flows from the boiler through a valve on the steam-pipe O, 
which is manoeuvred by the lever z m. 

R R, valves opening alternately. 

x, reservoir to supply water of condensation ; it receives 
water from the rising-pipe S, through a pipe governed by a float 
and stop-cock. 

y, pipe through which the cold water falls on the outside of 
the vessel P. 

n, gauge-cock to show the height of water in the boiler. 

25 



194 SAVARY — PAPIN. 

We have stated the more obvious defects of Savary's engine, 
as well as one which is not usually quoted. There is, how- 
ever, another of far greater importance, but which rests upon a 
physical principle, entirely unknown at the period in which he 
lived. This grows out of the necessity of filling the vessel al- 
ternately, with steam of high tension, and water of a low tem- 
perature. 

When the steam is first admitted into the vessel, it will be con- 
densed against its sides and upon the surface of the water ; nor 
will it begin to act mechanically until both be heated to the 
temperature of 212°. Its full effect will not take place until 
both are heated to such a degree as will maintain the sieam at 
a temperature, and consequent tension, appropriate to the height 
of the place of discharge. As the water is forced out of the ves- 
sel, fresh cold surfaces are exposed, and must be heated in their 
turn ; and when the vacuum is to be formed, the outside of the 
vessel is cooled by the affusion of water, while the inside is far- 
ther cooled by the rise of water from the reservoir beneath. In 
these different ways it has been found, by experiments carefully 
conducted, that ifths of the steam is condensed without acting 
at all, and that, of course, a similar proportion of fuel is wasted. 

The engine of Savary, therefore, is confined to a single ob- 
ject, namely, that of raising water ; and even this, for the rea- 
sons we have stated, it does to great disadvantage. Still, how- 
ever, the introduction of this engine was not only important as 
a step to the construction of more perfect ones, but it was of it- 
self of some value when compared with the methods for raising 
water that were at that period in use. 

145. An apparatus which, at first sight, bears a strong simi- 
larity to Savary's, was constructed by Papin, for the Elector of 
Hesse, in 1707. It differs in having a piston, working in the 
vessel into which the steam is alternately admitted and con- 
densed, and makes no important use of the pressure of the at- 
mosphere. It appears that, even with the aid of the celebrated 
Leibnitz, he had been unable to bring his cylinder engine to 
perfection, and had abandoned his researches until again sti- 
mulated by the success of Savary. 



PAPIN — NEWCOMEN AND CAWLEY. 

r e give a figure of this last engine of Papin. 



195 




a is the boiler, furnished with a safety valve b, pressed down 
by a weight c, suspended from a lever. Water is introduced 
into the boiler through this valve, fis the forcing vessel, hav- 
ing an aperture at the top closed by the valve g. A piston is 
placed in this vessel, having a socket into which a cylinder of 
iron z, heated red hot, is introduced to keep up the tempera- 
ture of the steam ; water is admitted into the forcing vessel 
through the funnel x, and valve h. The rising pipe k enters 
an air vessel. The action of the steam in the forcing vessel 
raises the water into the air vessel, whence, by the pressure of 
the condensed air, it runs in a continual stream ; when the 
piston has descended to the bottom of the vessel/, the valve d 
is closed, and no more steam flows over ; the valves e and g 
are opened ; through the former, the steam that has been used 
escapes, and through the latter the forcing vessel is again filled. 

146. The time had now arrived in which the world was to 
derive essential advantages from the employment of steam as a 
moving power. Even Savary's engine, although more valuable 
than any other we have hitherto spoken of, had obvious defects, 
which prevented its coming into general use. These obvious 
defects were remedied by the engine of Newcomen and Caw- 
ley, their patent for which issued in 1705. Departing from the 
idea entertained by all former inventors, except in the abortive 
proposition of Papin, of making the steam act directly to raise 
water, either by pressing upon its surface or by forming a va- 
cuum on its condensation, Newcomen and Cawley sought the 



196 NEWCOMEN AND CAWLEY. 

means of working the brake of a forcing pump. With this 
view, the pump-rod being loaded with a weight sufficient to 
bring it to rest in its lowest position, the brake or lever of the 
pump was made with equal arms, and resting on a pivot in the 
middle of its length. 

The pump-rod being thus loaded, and attached in this manner 
to one end of the beam, a piston, of size considerably larger than 
that of the pump, was attached to the other, and made to fit a 
Cylinder, at the upper end of which it rested, under the pre- 
ponderating weight of the pump-rod and its load. The Cylin- 
der had in its bottom a valve opening upwards, by which steam 
could be at pleasure admitted or cut off. To the side of the 
Cylinder and near its bottom was attached a horizontal pipe, 
bent upward at the open end : in this was placed a valve open- 
ing to the air, which is called the snifting valve. Steam of the 
temperature of 212° being admitted into the Cylinder, would, 
from its levity, rise to the upper part of that vessel, displace the 
air previously contained therein, which flows out through the 
latter valve, making a sound which has given this valve its 
name. If the steam that thus enters the Cylinder have its com- 
munication with the boiler closed, it may readily be condensed, 
and a partial vacuum formed, beneath the piston. The pres- 
sure of the atmosphere will now act, and force the piston down- 
wards to the bottom of the Cylinder ; the opposite end of the 
lever-beam will be raised, and with it the pump-rod, and the 
weight with which it is loaded. If the communication with 
the boiler be again opened, the pressure on the opposite sides 
of the piston will again become equal, and the preponderating 
weight of the pump-rod will cause it to descend, and draw up 
the piston to its primitive position. A second condensation will 
cause the piston again to descend, and the process may thus be 
kept up so long as the boiler continues to supply steam. 

The condensation in the Cylinder was at first produced by 
cooling the outside, by the affusion of cold water ; and, when 
the action was required to be rapid, by placing the cylinder in 
an external cylindrical space. A hole having been accidentally 
made near the bottom of the Cylinder, the water spouted into 
it, and the condensation was found to be much more rapid. 



NEWCOMEN AND CAWLEY. 197 

This was then imitated, by adapting a pipe to the Cylinder, 
through which a jet was made to flow as often as it was ne- 
cessary to condense the steam. This pipe and injection appa- 
ratus, were governed by a stop cock or valve placed upon it. 
Thus there were two valves necessary to the action of this en- 
gine, and these were to act alternately, the one opening as the 
other closed, and vice versa. 

147. In the original form of the engine these were worked 
by hand, a boy being placed within reach of the levers that 
opened and shut them, to perform that operation as often as 
necessary. This employment being excessively irksome, one 
of the persons was not slow to perceive that it might be per- 
formed, even better than it could be by any personal attention, 
by the alternating motion of the lever beam itself. This im- 
portant step towards the perfection of the engine was made by 
a boy of the name of Potter, and was immediately adapted to 
all the engines of Newcomen and Cawley. 

It will be at once obvious, that the steam in this engine was 
employed solely to form a vacuum by its condensation, and 
that the pressure of the atmosphere was the efficient agent. 
Hence, as Savary's patent comprized the use of steam for this 
purpose, he was associated in the profits of Newcomen and 
Cawley. 

As this was the sole use that was made of the steam, it was 
unnecessary to generate it of a tension greater than that of the 
atmosphere; hence its use became perfectly safe, while the 
height to which it was capable of raising water was as great 
as could be effected by a forcing pump worked by any agent 
whatsoever. This engine, therefore, far exceeded that of Sa- 
vary, both in its ease of application and its power. 

On the other hand, the principal physical defects, noted as 
affecting Savary's engine, were still inherent in Newcomen's, and 
its mechanical execution became far more difficult. So great, 
indeed, was the latter difficulty, in the then imperfect state of 
the arts, that it was found impossible to keep the piston tight, 
except by covering its surface with a mass of water, whose 
presence still farther enhanced the physical imperfections. 



198 NEWCOMEN AND CAWLEY. 

The steam being condensed within the Cylinder, the whole 
was cooled down at each stroke to the temperature of conden- 
sation ; while the part of the Cylinder above the piston in its 
lowest position, was still further cooled by the mass of water 
employed to render it tight. On the re-admission of the steam, 
the whole was again to be heated up to the boiling point ; thus 
the waste of fuel was quite as great as in the engine of Savary. 

Another imperfection grew out of the partial nature of the 
vacuum that it was possible to produce in the cylinder. Water 
which boils under the ordinary mean pressure of the atmos- 
phere at 212°, rises into vapour at all temperatures whatsoever, 
and boils at lower temperatures under diminished pressure. 
Hence, so soon as the piston began to descend, the action of at- 
mospheric pressure was lessened by the generation of fresh 
steam, and although this was in its turn condensed, its place 
would be. odcupied by new steam of a lower temperature, and a 
resistance would be opposed to the descent of the piston. 

In consequence of this retarding force, it was found in prac- 
tice impossible to make the pressure of the atmosphere, which 
is, at a mean, 151bs. per square inch, act upon the piston with 
a mean force of more than 17ilbs., and from this, in estimating 
the action of the machine, the friction, and other retarding forces, 
are to be deducted. This engine, therefore, consumed about 
twelve times as much fuel as would have generated steam suf- 
ficient to fill the Cylinder, and worked with but half the force 
the moving agent was capable of exerting. 

The rectilineal motion of the pump and piston rods was, in 
this engine, accommodated to the circular motion of the ends of 
the lever-beam, in a very simple and ingenious manner. 
The ends of the beam were made in the form of arcs of circles, 
and the rods were suspended from them by chains, attached to 
the highest point of each arc. Thus, as the active pressure of 
each of these, in the performance of its share of the work was 
vertically downwards, it was always applied directly to the 
beam, the two rods being respectively always in the direction 
of tangents to the circular arcs formed upon the working beam. 

148. The valve apparatus of Potter, called by him the Scog- 



NEWCOMEN AND CAWLEY. 



199 



gan, was, in 1718, superseded by a more perfect arrangement 
invented by Beighton. A frame or bar was attached by a chain, 
working also over a circular arc, to the lever beam ; projecting 
pieces or pins, forming a rack, were attached to the frame • the 
valves were moved by quadrants cut into teeth, and acting up- 
on a rack connected with the spindle of the valve ; to each of 
these quadrants was attached a lever, which was pressed by the 
pins upon the frame through a circular arc, until it passed the 
line of motion of the frame, and was disengaged ; from this 
position, the lever was made instantly to return to its original 
place, by the action of a weight. These levers being also fur- 
nished with handles, to enable the valves to be open and shut 
by hand, the apparatus was called the Hand Gear, the frame 
and pins, the Plug Frame. This mode of working the valves 
continued to be used up to the beginning of the present centu- 
ry, with but little improvement ; nor has it yet fallen wholly 
into disuse. 

The engine of Newcomen is exhibited in the annexed draw- 




200 SMEATON — LEUPOLD. 

ing, by which its mode of action and the uses of its several 
parts may be better understood. 

a is the boiler. 

t, the steam pipe. 

e, the steam valve. 

c, the Cylinder, into which the injection water is seen play- 
ing through the valve and pipe p. 

r, the piston. 

s, the snifting valve. 

m, a reservoir of water, whence the injection pipe is supplied 
and water flows, through the pipe n, to keep the piston tight. 

The injection water is discharged through the pipe i, and the 
excess of that floating on the piston by the pipe h. 

w is the weight attached to the pump-rod, by the action of 
which the piston is returned to its highest position. 

The lever beam and pump are too obvious to need descrip- 
tion. 

149. The engine of Newcomen and Cawley was improved 
in its mechanical structure by Smeaton, arid derived additional 
force from the general improvement of the mechanic arts. 
Smeaton also formed tables of the dimensions of the several 
parts. With these improvements it is still occasionally used, 
particularly in places where fuel is cheap and abundant ; where 
its small cost, and its safety, are considered as more than coun- 
terbalancing the great waste of fuel with which it is attended. 

150. In 1718, a German engineer, of the name of Leupold, 
published a work containing a description of two engines, the 
merit of which he ascribes to Papin. They are, however, ra- 
ther to be considered as ingenious applications of his own, of 
the principle of that inventor, aided by the knowledge of what 
had been effected by Savary and Newcomen. In one of these 
the steam was made to act alternately upon the surface of water 
in two vessels, and it is so similar in every thing, but the form 
and position of its parts, to the engine of Savary, that we do not 
conceive it necessary to describe it minutely. The second is a 
high pressure engine with pistons, and is extremely ingenious. 



LEUPOLD. 



201 



besides being remarkable as the first in which steam of high 
tension was made to act upon a piston. The first of these is 
liable to all the objections that we stated in speaking of Savary's 
engine. The second is far better, and even preferable in many 
respects to the engine of Newcomen. It is, besides, applicable 
to the production of a continuous rotary motion, and is there- 
fore the first that could have been applied to general purposes 
in the arts. Of this last engine we have in consequence given 
a figure. 




Steam is generated in the boiler c, and flows thence through 
the pipe d ; it is represented as passing through one of the pas- 
sages in a four-way cock, beneath the piston a, while the steam 
which had filled the other cylinder is escaping into the air 
through the passage e. The piston a works a lever and the 
pump-rod g, while b works another lever and the pump-rod/. 

h is the fire-place. 

The two pumps force water alternately into the rising pipez. 

26 



202 LEUPOLD. 

Did the levers act upon eranks situated upon the same axis, 
a continuous rotary motion might be produced. 

Steam in this case is the moving power, and is not condens- 
ed as in the engine of Savary. It, therefore, is constantly retard- 
ed by the pressure of an atmosphere, and must have a tension 
of at least two atmospheres in order to work to advantage. 

The history of the steam engine is thus brought down, from 
the most remote period at which the power of that agent was 
first suspected, until it assumed a definite form, and became ca- 
pable of useful application. Hitherto, however, but one spe- 
cies of work came directly within its scope. In the succeeding 
chapter we shall find its physical defects remedied or removed, 
and its application finally made universal to every species of 
manufacturing industry. 



CHAPTER VIII. 

CONCLUSION OF THE HISTORY OP THE STEAM ENGINE. 

Power and Dejects of Newcomers Engine. — Birth and Edu- 
cation of Watt. — Professor Robison. — Watt's first experi- 
ment. — Professor Anderson. — Watts second experiment. 
— Inferences. — Separate Condenser. — Steam applied as 
the moving power. — Packing. — Jacket and Air-pump. — 
Working Model. — Dr. Roebuck. — Experimental Engine. 
- — -Watt's first patent. — Gainsborough's claim. — Boring 
apparatus. — Form of Watt's first Engine. — Saving of 
Fuel. — Projects for rotary motion. — Fiztgerald, Stewart, 
and Clarke. — Double-acting Engine of Watt. — Wash- 
borough and Pickard. — Crank. — Sun and Planet Wheel. 
Other Inventions and Improvements of Watt. — Hornblower. 
— Watt's patent extended. — Governor. — Introduction of 
steam into various mechanic arts. — Expiration of Watt's 
patent. — Cartwright and Sadler. — Murray, Maudslay, 
and Fulton. — Woolfe. — Oliver Evans. — Trevithick and 
Vivian. — Rotary Engines. — Conclusion. 

151. In the preceding chapter the prominent defects of the 
engine of Newcomen and Cavvley have been pointed out. In 
spite of these, it had been found of immense value in practice, 
in raising water for the supply of cities, and more particularly 
in draining mines. So great, indeed, had been the advantages 
derived from it in these cases, that hopes had been from time to 
time entertained that this engine might be rendered efficient in 
performing work of other descriptions ; and it had even been 
thought of as the prime means of propelling boats. That the 
energy of the prime mover was adequate to any of these pur- 



204 WATT. 

poses was certain, but mechanical difficulties opposed its appli- 
cation. Even had these been overcome, the engine was liable 
to physical imperfections, which had not at this period been sus- 
pected, far more formidable than those which are merely me- 
chanical. The latter, we now know, are so great in amount, 
as to have prevented the atmospheric engine from competing 
with almost any other prime mover, except in a few particular 
cases. These objections, whether physical or mechanical, 
might have been gradually removed; the former by the gene- 
ral progress of the arts, the latter by the discoveries in physical 
sciences with which the close of the last century teemed. The 
steam engine, however, was not destined to wait for the slow 
changes which follow the application of purely theoretic prin- 
ciples to practical purposes. A single individual was found, 
who, by his own researches and unaided efforts, reached the 
law of the relations of steam to heat, which was, about the same 
time, discovered in its more general form by Dr. Black. This 
illustrious individual was James Watt. 

152. Watt was the son of respectable, but poor parents. His 
grandfather exercised the profession of a schoolmaster, his fa- 
ther that of a merchant in Greenock, in Scotland. Having re- 
ceived the elements of a liberal education, which the excellent 
school system of Scotland places within the reach of all, Watt, 
at the early age of sixteen, became the apprentice of a maker of 
optical instruments in the city of Glasgow. Two years after- 
wards he removed to London, and obtained employment from 
a maker of mathematical and philosophical instruments. In 
this employment, his health became affected, and he was com- 
pelled to return to his native district. 

In undertaking business on his own account, he would have 
preferred Glasgow, as offering far greater prospects of success 
than Greenock, and hence became anxious to settle in the for- 
mer place. To this plan, however, obstacles presented them- 
selves, in the form of the laws of the corporation, by which the 
exercise of a trade was restricted to those entitled to the privi- 
leges of a burgess, to which Watt had no claim. From this 
state of difficulty he was fortunately relieved' by the interposi- 



ROBISON ANDERSON. 205 

tion of the professors of the University. This institution pos- 
sessed, as a remnant of ancient privileges, the right of claiming 
immunity from the corporate restrictions, and Watt was furnish- 
ed by them with apartments within the college buildings, in 
which he pursued his trade. 

153. His attention was first called to the subject of steam by 
Professor Robison, then a student of the University of Glasgow, 
at a date as early as the year 1759 ; but their researches were 
attended with no important advances. 

154. In 1761, Watt made experiments with an apparatus re- 
sembling the engine of Leupold ; but becoming aware of the dan- 
ger attending the use of high steam on a large scale, he ceased 
from any farther pursuit in that direction. 

155. In 1764 he was employed by Professor Anderson, then 
holding the chair of mechanical philosophy in that institution, 
to repair a working model of Newcomen's engine. The obvi- 
ous waste of steam that he found to attend the action of this 
model, and the great quantity of injection water it required, 
struck him as facts unaccounted for by any previous scientific 
reason. Suspecting that the first defect might arise from an er- 
roneous estimate of the comparative densities of steam and wa- 
ter, he, by a few simple experiments, endeavoured to ascertain 
the true relation, and found that water in becoming steam ex- 
pands itself, under ordinary pressures, to 17 or 1800 times the 
bulk it had previously occupied. This is not far from the 
truth, as we now know from more accurate experiments, and 
corresponded with the estimate of Smeaton. At this density 
for steam, his experiments shewed that six times as much 
steam, as was simply sufficient to fill the Cylinder, was expend- 
ed at each stroke of the piston. He at once attributed this 
increased expenditure to the cooling of the Cylinder. The 
great quantity of injection water next engaged his attention, 
and the high heat the Cylinder retained in spite of the large 
quantity admitted. By adapting a bent tube to a common tea- 
kettle, and immersing the end of the tube in a vessel of cold wa- 



206 BLACK. 

ter, he passed steam from the kettle into the cold water, by 
which the steam was condensed. The temperature of the wa- 
ter was increased by the heat of the condensed steam ; and by 
inquiring into the gain of weight which had taken place when 
the water reached the boiling point, he inferred that it required 
six times the weight of the steam simply to effect its condensa- 
tion, without lowering its temperature, or, that 1800 measures 
of steam were capable of heating six measures of water to their 
own temperature, although the 1800 measures are derived from 
no more than one measure of water. Thus he reached experi- 
mentally one of the most important facts of the doctrine of la- 
tent heat, a doctrine which had been that very year taught in 
the same institution, for the first time, by Dr. Black. On com- 
municating the result of his observation to that distinguished 
chemist, he received from him an explanation of that doctrine, 
which furnished the confirmation and rationale of the pheno- 
menon he had observed. 

His experiments also shewed him that the pressure of steam 
increased nearly in geometric progression, while its tempera- 
ture was raised in arithmetic. The decrease of tension at low- 
er temperatures follows a similar law ; and hence the pressure 
of the atmosphere on the piston never acted with a force great- 
er than eight pounds per square inch. 

156. Thus, then, the cause of the imperfections of Newco- 
men's engine became apparent at one and the same time, by 
the aid of actual experiment, and by the application of the ge- 
neral theory of Black. But it was far less easy to point out the 
remedy for these defects than to discover the cause. It was 
evident, that to obtain all the power the steam was capable of 
exerting, the Cylinder should not be colder than the steam 
which entered it ; while, on the other hand, the condensed steam 
should not raise the injection water above the temperature of 
100° at the very outside, while a lower temperature would be 
preferable. The mode which he adopted, of meeting these two 
requisites, is as simple as it is ingenious ; yet it was not attain- 
ed without great study and reflection on his part. 



WATT. 207 

157. It was not until a year after his performance of the ex- 
periments we have spoken of, that it occurred to him that if a 
communication were opened between the Cylinder of the steam 
engine, and another vessel exhausted of air, the steam would 
rush suddenly into the empty vessel ; and that, provided the 
latter were kept cool by being immersed in water, or by injec- 
tion, the steam would continue to flow until the whole were 
condensed. 

158. With this idea he appears to have entertained, at the 
same time, the intention of using steam itself as the moving 
power instead of atmospheric pressure, and his experiments on 
its elasticity had shown him that a small increase in its tempe- 
rature would probably give a very considerable addition of pow- 
er. To effect the latter part of his plan, it would be necessary 
to make the piston-rod work air-tight, through a lid or cover 
adapted to the cylinder. A modification of the common air- 
pump had an arrangement that served as a model of the latter 
method, the barrel being covered by a lid, having at its centre 
a collar of leathers, by which the passage for the pump-rod was 
rendered air-tight. 

159. It next became obvious that the piston could not be 
rendered tight in this case by keeping a mass of water floating 
upon its surface, for this liquid would have been speedily eva- 
porated, and would have wasted much heat. Hence, more per- 
fect workmanship would be required, and the packing must be 
moistened with a liquid that did not boil, except at a tempera- 
ture higher than that to which the steam was ever raised. Oil 
is a liquid of this description ; but tallow, which becomes fluid 
at a temperature below that of ordinary steam, is still better. It 
is said that he originally proposed a packing of leather, but as 
this substance chars and cranks at a comparatively low temper- 
ature, it is unfit for the purpose, and bands of hemp were em- 
ployed in its stead. 

160. To keep the cylinder from losing heat too rapidly, he 
conceived the idea of enclosing it in the Jacket. 



208 WATT — ROEBUCK. 

Two methods occurred to him of keeping up a vacuum in 
the condenser. The first was that of adapting a pipe thirty- 
four feet in length, plunging at its lower end into a reservoir of 
water ; the second, that of exhausting the vessel hy a pump. 
The former being applicable in but few cases, he chose the lat- 
ter for general use ; and we have, indeed, no instance of the 
first being applied in practice. 

161. These views were submitted to the test of experiment, 
first in an apparatus of small size, and finally in a working 
model, whose Cylinder was nine inches in diameter. The re- 
sults were as satisfactory as his most sanguine expectations 
could have anticipated, and convinced him that he had dis- 
covered the means by which all the physical defects of the 
ancient engines could be remedied ; the steam no longer wasted 
by admission into a cylinder cooled by injection ; and a va- 
cuum far more perfect obtained, than had ever been before 
reached. 

The expense of constructing a steam engine, and the difficul- 
ty of inducing capitalists to embark in an untried scheme, 
seems to have deterred him from bringing it forward ; and he 
devoted himself, for upwards of three years more, to pursuits 
far beneath the powers of his mind. 

162. It is, even at the present day, rare to find in men whol- 
ly devoted to business pursuits that acquaintance with physi- 
cal principles which will enable them to judge of the merits of 
an improvement in the arts that rests wholly on those princi- 
ples. And such was the invention of Watt, which differed, as 
far as superficial examination could reach, from the engine of 
Newcomen, only in the addition of a cumbrous appendage, of 
which the light of physical science alone could exhibit the 
appropriate use, and manifest all the importance. For informa- 
tion of that description it was in vain to seek among the tra- 
ders of Glasgow at that early period, and Watt wisely determin- 
ed to keep his discovery to himself until he could meet with a 
person qualified to appreciate its merits. Such a coadjutor he 
at last found in the celebrated Dr. Roebuck, a person to whom 



ROEBUCK — BOLTON. 209 

Great Britain is under great obligations as the founder of the 
Carron works, in which the manufacture and application of 
cast iron was brought to that degree of perfection, which has 
added so much to the wealth of that country. 

Educated in the most liberal manner, and for a learned pro- 
fession, he became an adept in all the chemical and physical 
sciences of the day, and had applied his knowledge to the es- 
tablishment of a chemical manufacture whence he was deriving 
enormous profits. These he undertook to apply to mining for 
coal and iron at Kinneil, and to the establishment of the cele- 
brated manufactory of iron, of which we have spoken. 

163. His scientific intelligence at once appreciated the whole 
merit of Watt's improvement, and he gladly furnished the funds 
for constructing an experimental engine, which was tried in 
the drawing of water from one of the mines at Kinneil. This 
engine worked as well as had been anticipated, and Watt was 
furnished by Roebuck with the means of securing his inven- 
tion from piracy, in the form of a patent. 

In return for his advances, Roebuck became joint proprietor 
of the patent, and from his capital and influence, Watt had rea- 
son to hope for the speedy introduction of his invention into 
general use. But Roebuck had embarked in schemes be- 
yond the reach of his finances, and of these, one, so far from 
being profitable, was ruinous to his fortune. The Carron 
works indeed flourished, but the mining speculation made no re- 
turns ; and so far from being able to assist Watt any further, he 
was himself compelled to abandon, not only his least promising 
scheme, but also that which was going on successfully, and thus 
to leave to others to profit by the fruits of his intelligence and 
enterprize. In the wreck of his affairs, his share of Watt's pa- 
tent passed into the hands of his friend Bolton of Birmingham. 
This skilful and enterprising merchant was not only well 
qualified to appreciate the merit of Watt's invention, but pos- 
sessed the capital, by the aid of which alone it could be brought 
into successful operation. 

164. The first patent of Watt is dated in March, 1769, and 

27 



210 GAINSBOROUGH — WATT. 

when an application was made to Parliament for its extension, 
opposition was made, on the plea that the most important part 
of his invention, the separate condenser, had been invented at 
a period at least as early as the date of the patent, by a person 
of the name of Gainsborough. This claim was, however, set 
aside in consequence of clear and decided proof that Watt's 
method was not only original with him, but earlier in date. 

165. It does not appear that any other of the methods by 
which Watt had rendered his engine so superior to all former 
ones, had occurred to Gainsborough or any other person. Still 
we have no reason to doubt that Gainsborough had actually, 
and by investigations of his own, reached the plan of a separate 
condenser ; and we cannot but believe that the study of the 
doctrine of latent heat might have led others, at a date not 
much later, to a similar discovery. That the improvements in 
physical science had rendered the world ripe for the introduc- 
tion of Watt's invention, need be no diminution of his great 
merit ; for, if not the only one who thought of the remedies we 
have mentioned above, he was undoubtedly the first, and prior 
by several years to any other person. Nor is it merely by pri- 
ority of invention that Watt is to be distinguished ; there was a 
finish and completeness about every plan that emanated from 
his mind, which suited it at once for practical usefulness. 

This, indeed, was a peculiar trait of the genius of Watt ; in- 
vention was with him so much a habit, that he rarely examin- 
ed any project without suggesting improvements ; while caution, 
almost amounting to timidity, led him to keep back from the 
world his own discoveries until he felt assured of their suc- 
cess. This excess of caution would probably have retarded, 
if not wholly prevented his success, had he not been fortunate in 
his connexion with a partner, who possessed the boldest spirit of 
mercantile enterprize, united to the most consummate judg- 
ment and prudence. In this point of view we may consider the 
world as being almost as much indebted to the intelligence and 
business ability of Bolton as to the genius of Watt. 

English writers have spoken of Watt as illiterate and defi- 
cient in education. If he is to be judged by the standard of 



WATT. 211 

classical knowledge, to which alone the name of learning is 
given in that country, the assertion might be true. But we 
should rather be inclined to cite him as an instance of an edu- 
cation exactly directed to the purpose of rendering him useful 
in the important career to which he was called. The public 
schools of Scotland, if the mere pedantry of classical knowledge 
be neglected, give that species of instruction which extends the 
power of using the vernacular tongue for all business and prac- 
tical purposes ; Watt, besides, became a good practical geometer, 
and his early pursuits compelled him to be acquainted with all 
the physical science that was then known. When to this was 
added practical skill in mechanical operations, we cannot but 
think that Watt had derived from education that knowledge 
which was exactly suited to render him eminent. 

166. We have stated that the engine of Watt dispensed with 
the use of water for the purpose of keeping the piston tight, 
and that a greater degree of accuracy was in consequence re- 
quired in the workmanship. The Cylinders of steam engines 
are cast hollow, by means of a core that fills up a part of the 
mould. They are then reamed out, and brought to the proper 
size by means of a borer, or tool affixed to a revolving axis. 
Great improvements in the boring of Cylinders were introduc- 
ed by Smeaton at the Carron works, but the method was not, 
at the date of Watt's patent, so perfect, as to give the interior a 
form wholly independent of the original shape of the cavity. 
But Watt had the advantage of receiving, just as he was about 
establishing a manufacture of steam engines at Bolton's works 
of Soho, near Birmingham, a new method of boring. This was 
the invention of Mr. John Wilkinson, a proprietor of iron works, 
at Birsham, near Chester. Watt immediately availed himself 
of this improvement, and was, by means of it, enabled to furnish 
Cylinders of a perfection of workmanship that had previously 
been despaired of. In a Cylinder of fifty inches diameter, con- 
structed by him at an early date, the greatest error was less than 
the sixteenth part of an inch. This perfection of workmanship 
was almost essential to the introduction of steam into general 
use, as a prime-mover ofmachinery ; for, although the process 



212 WATT. 

of raising water had been, and might still have been, effected 
with advantage by Cylinders of less accuracy, the durability of 
the engine would, even in this very limited application of its 
powers, have been lessened, while the delicate operations it now 
performs would have been impracticable. This method of 
boring was still further improved, until a six foot Cylinder 
could be bored, with no error greater than the fortieth part of 
an inch. 

167. In the first engine of Watt, the piston was attached by 
chains to the lever beam, from the opposite end of which the 
pump-rod, loaded with a weight, hung. The primitive posi- 
tion of the instrument is therefore the same as in that of New- 
comen, namely, the pump-rod preponderates, and holds the pis- 
ton in its highest attainable position. The engine has three 
valves, by one of which steam is admitted beneath the piston 
into the Cylinder, where it displaces the air, and fills its cavity 
wholly. So soon as the Cylinder is thus filled with steam, 
this valve is shut, and the remaining two are opened ; through 
one of these the steam passes into the condenser, which acts to 
convert the steam into water, partly in consequence of the cold- 
ness of its sides kept constantly immersed in a cistern of water, 
and partly by the aid of a jet of injection water ; through the 
other valve, steam flows from the boiler and presses down the 
piston, thus causing a motion at the opposite end of the beam, and 
raising the pump-rod. The piston having reached its lowest 
position, these two valves are closed. It thus becomes neces- 
sary that the piston should be again raised to its original position 
by the weight attached to the pump-rod. This might have been 
done by allowing the steam situated above the piston to escape 
into the air, and permitting steam to flow into the lower part of 
the Cylinder. The pressure on both sides of the piston being 
thus nearly equalized, the weight would have preponderated and 
raised the piston. But in this case a Cylinder full of steam would 
be condensed at each descent of the piston, and another allow- 
ed to escape, without effect, at each ascent. The waste of the 
last-mentioned quantity of steam was thus obviated by Watt ; 
& pipe was adapted to the side of the Cylinder ; in this the two 



watt's single engine. 213 

steam valves were placed so that the communication, from the 
lower of these valves with the boiler, could only be effected by 
opening the upper one. Hence, in first filling the Cylinder, 
both of these valves must be opened at once ; in all other cases 
they act alternately. The upper valve was placed above the 
passage by which steam enters into the upper end of the Cylin- 
der, and thus only the lower steam valve intervened between 
the steam acting on the piston from above, and that rushing 
into the condenser from below. The piston having reached 
its lowest position, the steam and condensing valves are shut, 
and the valve in the side pipe is opened ; a communication is 
thus made between the steam above the piston, and the part of 
the cylinder beneath it, the weight of the pump-rod then acting 
upon the piston, will meet no other opposition than the friction 
of the piston itself, and the resistance which the steam experi- 
ences in passing through a pipe ; the weight will therefore pre- 
ponderate, the piston will be drawn up, and the steam will cir- 
culate from the upper side of the piston through the side pipe, 
and fill the space beneath the piston. 

The upper valve alone is a steam- valve, except when the en- 
gine is to be set in motion ; at which time the second valve is 
opened with it, and admits steam to the lower part of the cylin- 
der. In all other cases the latter is merely a valve of commu- 
nication, and may be called the equilibrium valve. The third 
valve may be called the condensing valve. 

This arrangement may be better understood by the inspec- 
tion of the following figure, and the uses of the parts will be 
understood by reference to the description of the double-acting 
engine. 



214 



watt's single engine. 




WATTS SINGLE ENGINE. 215 

a, Cylinder. 

b, Piston represented in its primitive position. 

c, Steam- valve. 

d, Steam-pipe. 

e, Equilibrium-valve. 
/, Condensing-valve. 

g, Pipe leading to condenser. 

h, Condenser. 

i, Air-pump. 

k. Hot- water cistern. 

I, Air-pump rod. 

m. m, m, Hand Gear. 

n. 71, n, Tappets of the Plug-frame. 

o, Side-pipe. 

p, Hot-water pump, 

q, Cold-water pump. 

r, Cold-water cistern. 

s, Foot-valve. 

w, x, Piston-rod, working in a stuffing-box at w. 

y, Working-beam. 

168. Still further to diminish the loss of heat, Watt pumped 
back the water of condensation into the boiler ; by these several 
improvements so great a saving of fuel was obtained, that the pa- 
tentees asked no other remuneration for the use of the invention, 
except one-third part of the value of this saving. In a single 
mine in Cornwall, where three of their engines were employed, 
this compensation was commuted for £8000 sterling per an- 
num. 

The valves still continued to be opened and shut by an ap- 
paratus similar to the plug-frame and hand-gear of Beighton, 
but improved, and rendered more easy in its action ; the former 
became a part of the rod of the pump by which the vacuum of 
the condenser was maintained. The pump and piston-rods 
were still suspended by chains from circular arcs forming parts 
of the lever-beams, and the air-pump rod was suspended in the 
same manner ; the latter, therefore, required a weight to return 
it downwards, after it had been raised by the beam. 



216 STEWART — CLARKE. 

The condenser and pump underwent various modifications 
before Watt was satisfied with their action, and finally assum- 
ed the form described in treating of the double-acting engine. 

169. Previous to the time of Watt, there had been but little 
demand for steam, as a moving power, for any other purpose 
than that of raising water ; and for several years after his first 
researches, the state of the manufactures of England was not 
such as to require powers beyond what could be obtained from 
natural waterfalls or the action of the wind. Savary had, in- 
deed, proposed to make the water raised by his apparatus fall 
upon an over-shot wheel, and thus to apply the power of steam 
to any manufacturing purpose whatever. Similar projects 
had been entertained in relation to the engine of Newcomen. 
Neither of these, however, could have been applied to any ad- 
vantage, in consequence of the great cost of fuel they must have 
occasioned, particularly as the effective power of a wheel is 
considerably less than the absolute mechanical force of the water 
employed. 

The several projects of steam-boats that we shall hereafter 
speak of, necessarily required rotary motions ; but these were all 
imperfect and abortive. Leupold's engine alone, had the two 
pistons been applied to cranks situated upon the same axis, 
could have produced a rotary motion ; but the inventor does 
not appear to have been aware of the value of this part of his 
own invention, or at least did not consider this application of it 
of importance. 

170. In 1757, a person of the name of Fitzgerald attempted 
to take off a rotary motion from the piston of Newcomen's en- 
gine by means of ratchet-wheels, that could be forced forwards 
during the descent of the piston, but would remain fixed dur- 
ing its ascent. The continuity of the motion was to be kept 
up by a fly-wheel. This was too imperfect a method to be suc- 
cesful, and had no result. A similar project was entertained 
by persons of the names of Stewart and Clarke, who attempted 
to apply it to sugar mills in Jamaica ; but this, like the other, was 
abandoned as impracticable or useless. Still later, at a colliery 



watt's double engine. 217 

in England, a drum for raising coal had been worked by an at- 
mospheric engine, but even this rude apparatus was but imper- 
fectly driven. Hence it was left for Watt to fit the steam en- 
gine for general use, as well as to improve it in its application 
to the sole purpose in which its energies had been successful 
before his day. 

171. The first step towards making the steam engine capable 
of producing a continuous motion in machinery, was to make 
the piston work during its ascent as well as its descent ; for both 
in the atmospheric engine, and the first engine of Watt, the 
moving power is exerted only to press down the piston, which 
is afterwards returned to its- original position by the action of a 
counterpoise. 

Watt, whose caution was equal to his genius, proceeded in 
his inventions by slow and gradual steps. His first engine 
hardly varied from Newcomen's in external form, and was, in 
truth, rather a great and all-important improvement upon that 
imperfect apparatus, than an invention absolutely original. In 
the same manner his double-acting engine was obtained by a 
slight and simple alteration of his former one. It was required 
that the piston should be forced upwards as well as downwards 
by the steam; he effected this by adding one additional valve 
to the three employed in his single-acting engine. The equili- 
brium valve of the single engine became a steam valve, instead 
of serving as a mere communication between the opposite sides 
of the piston, and the valve that was added was one forming a 
communication between the condenser and the upper part of 
the cylinder. Hence it was necessary that the steam-pipe should 
extend to the lower pair of valves, and the condensing pipe to 
the upper ; the side pipe was thus doubled. The improved 
hand gear of Beighton was still retained, to open and shut the 
valves. 

The mode of operation of this engine has already been fully 
explained, it is therefore unnecessary to repeat it here. But it 
did not at first assume the perfect form in which it has been re- 
presented in chapter IV. The steps by which Watt proceeded 
were as follows. The rectilineal motion of the piston-rod hav- 

28 



218 WASHBOROLGH — PICKARD. 

ing been rendered capable of exerting an equal force, both dur- 
ing its ascent and descent, a connexion with the beams by- 
chains was no longer sufficient ; for although they would be 
efficient in drawing the beam downwards, their flexibility- 
would not admit of their forcing it upwards. It hence became 
necessary that their connexion should be made of a rigid mate- 
rial, and yet in such a manner as to permit the rectilineal motion 
of the one to accommodate itself to the circular motion of the 
other. True to his general system of slow and cautious im- 
provement, Watt attempted at first no violent alteration. The 
circular end of the lever beam was merely cut into teeth, or ra- 
ther had a toothed segment bolted to it, and for the chain a 
rack was substituted, which caught into the teeth of the seg- 
ment. Thus the stroke of the piston became effective, both 
during its ascent and descent. It will be obvious, however, 
that this is a rude and imperfect method, and he speedily con- 
trived a better in the shape of the parallel motion: 

172. About the time that Watt undertook to adapt his prin- 
ciple to general purposes, an engineer of the name of Washbo- 
rough attempted to attain a similar end, by means of the atmos- 
pheric engine. His plan was very similar to Fitzgerald's, and 
was improved by Pickard. Engines of their joint construction 
came into use in Gloucestershire, and at the block manufactory 
of Mr. Taylor at Southampton. The first actual application 
of the crank to the steam engine seems to have been due to 
Pickard. 

173. Watt however, at an earlier date, conceived the idea of 
making two single-acting cylinders act upon cranks situated 
upon the same axis, and thus produce a continuous rotary mo- 
tion. In the attention which the introduction of his engine 
into use for raising water required, this idea was suffered to re- 
main unimproved until he had completed the plan of making the 
engine double-acting, and of communicating the motion of its 
piston to the beam, by the rack and toothed segment. To ap- 
ply the motion thus obtained to general purposes, it became ne- 
cessary to convert the reciprocating motion of the beam into 



CRANK. 219 

one continuous and rotary. That a crank was the most sim- 
ple and obvious means of performing this has already been 
shown, and Watt recurred at once to the idea we have stated 
above, as having suggested itself to him, except that in the 
double-acting engine but one crank would be necessary. Va- 
rious simple and familiar instruments have rotary motions, that 
are produced by this instrument. Among these may be men- 
tioned, as of most frequent occurrence, the Potter's wheel ; the 
turning lathe ; and a variety of the spinning-wheel, then in 
constant use, although now nearly obsolete. The friends of 
Watt assert that his views were communicated by a workman, 
who passed from his employ to that of Pickard ; but there is no 
reason why both may have not fallen upon the same simple and 
obvious plan of producing the same kind of motion. Be this 
as it may, Pickard took out a patent for the application of the 
crank to produce a rotary motion in the Steam Engine, and 
Watt, satisfied that his own ingenuity could provide a substi- 
tute, did not attempt to contest it, but left it as an obstacle in 
the way of his other competitors. 

174. To produce the effect that the crank was intended to 
perform, he adapted to his engines an apparatus called by him 
the sun-planet wheel. This is represented on the following 
page. 



220 



SUN-PLANET WHEEL. 




x, Connecting Rod. 
| z< z, Fly-wheel. 

a, "Wheel fixed upon the axis of the fly-wheel. 

b, Wheel revolving upon a pivot at the extremity of the con- 
necting-rod. 

The wheels a and b, having equal radii, whose sum is equal 
to the length of the stroke of the engine, the teeth of the wheel 
b will apply themselves to those of the wheel a, during the 
whole motion of the engine. The wheel b will turn the wheel 
a around, and cause the axis of the wheel, to which the latter is 
attached, to revolve. 

It will be obvious that the axis of the fixed wheel must re- 
volve twice as fast when driven in this manner as it does when 
propelled by means of a crank ; there are, in consequence, cases 
where it may be better suited to the required work than the 



WATT. 221 

crank ; such was the case in the earlier adaptations of Watt's 
engine to manufacturing purposes. When, however, in his sub- 
sequent engines, a crank furnished a better and more suitable 
speed, he did not hesitate to employ it. confident in the priority 
of his own claim to its application. 

175. We have thus seen Watt taking up the engine in a very 
imperfect state, gradually perfecting it in its application to its 
ancient purpose, and finally rendering it universal in its uses. 
He also made many accessory improvements, by which its use 
was rendered more easy and certain. Of these we may parti- 
cularize the steam-guage, the barometer guage for the vacuum 
of the condenser, the self-acting feeding apparatus, the self-regu- 
lating damper, and the form of boiler which is yet most general- 
ly employed with double-acting condensing engines. 

Under his directions the hand-gear of Beighton was first im- 
proved, and finally superseded by the eccentric, and the long 
slide valve was introduced. The eccentric and slide valve were 
claimed also by Murray of Leeds; but although he may, perhaps, 
be entitled to the merits of a separate discovery, Watt was suc- 
cessful in showing the priority of his own claim to them. 

After the parallel motion was added to the engine, the beam 
still continued to be of wood, as was the connecting rod. Subse- 
quent steps led to the substitution of the more inflexible materi- 
al cast-iron, and the pivots of the parallel motion, instead of be- 
ing, as before, placed beneath the beam, were now cast upon it, 
and turned down to the proper size and shape. Frames and 
pillars of iron to support the beam were gradually substituted 
for the floors of buildings and walls, that were at first used ; 
brass boxes forming the sockets for all the circular motions were 
introduced ; and the external beauty of the machinery improv- 
ed by perfection of finish, that added equally to the power and 
durability of the engine. It was in 1778 that Watt made the 
piston act during both its motions, and he did not cease, to the 
very end of his life, to extend its usefulness and improve its 
structure. 

No valuable addition to the condensing engine was made ex- 
cept by himself, or under his direction, if we leave out those of 



222 HORNBLOWER. 

Murray, which we have mentioned, and to which Watt was 
able to substantiate an earlier and more authentic claim. 

176. The application of steam acting expansively is also due 
to Watt. One of his single engines employed it in this man- 
ner at Soho as early as 1776 ; and he used it also in his double- 
acting engines almost from their first construction. We have 
seen, in another place, that he did not reap all the advantages 
of which this method is capable, nor was he permitted to hold 
it, as an invention of his own, without contest. Two brothers 
of the name of Hornblower, in 1782 took out a patent for the 
use of the same principle, but by means of two Cylinders. In 
the first of these the steam acts by its tension, and produces an 
effect equal to that which it does in the high pressure engine. 
On escaping from this it enters a second and larger Cylinder, 
in which it expands, and from the opposite side of whose piston 
the steam flows alternately to the condenser. Thus, then, the 
resistance which the atmosphere opposes to high steam, is re- 
moved, and the effect of its expansion brought into play. As 
the separate condenser interfered with the patent right of Watt, 
this plan could not be brought into use, nor was it desirable that 
it should; for an engine of equal power on this construction is 
more costly than that of Watt, and it is difficult to make the 
two Cylinders employed, one containing high the other expan- 
sive steam, act in such harmony, that one of them shall not be 
retarded by the other. 

177. Five years of Watt's patent had run out before he had 
fairly introduced his single engine into use. He therefore made 
application, in 1775, for an extension of the usual period, and 
the application was, after much opposition, granted. Thus, by a 
noble effort of national generosity the profits of his discovery 
were secured to him for a term of years sufficient to remune- 
rate him for his labours and sacrifices. The patent-right thus ex- 
tended became the object of a series of attacks, leading to judi- 
cial investigation ; but in spite of the interested and continual 
opposition, the patent was in every case maintained. 

It is, indeed, highly to the credit of the institutions of Great 



CONICAL PENDULUM. 223 

Britain that this long contest should, in all its points, have been 
constantly decided in favour of him to whom the world, after 
an interval that has deadened all partial feeling, assigns unani- 
mously the merit of discovery. Such an honourable result, we 
fear, could hardly have been attained in our own country, in 
which the most carefully guarded patent-rights are proverbially 
insecure, and those inventions which have added most to the 
national wealth, have been those that have been of least pecuni- 
ary value to the inventors. 

A conical pendulum had been applied to mills of various des- 
criptions before the time of Watt. The suggestion of the valu- 
able use to which it might be applied in the steam engine, is 
said to be due to a Mr. Clarke of Manchester ; we do not, how- 
ever, know whether he ever applied it in practice. It was, whe- 
ther as an original invention of his own or not, speedily adopt- 
ed by Watt, and adapted to all his engines where regularity of 
motion is needed. 

178. The patent for Watt's double-acting engine is dated in 
1782, and in the same year one was erected at the Bradley Iron 
Works on this principle. It had the toothed segment on the 
lever beam, and a rack attached to the piston-rod. Since that 
period the improved engine has been introduced to a very great 
extent in the manufacture of iron; for impelling the blowing 
apparatus in blast furnaces, and for rolling, hammering, and 
slitting wrought iron. 

The patent for the parallel motion was issued in 1784, and 
in that year the Albion Flour Mills were erected in London. 

Two of Watt's double-acting engines, of 50 horse power each, 
were applied to drive twenty run of mill stones ; the establish- 
ment was conducted with great profit until the year 1791, when 
the building, with all the machinery and stock, was consumed by 
fire. It was suspected at the time to be the work of an incen- 
diary, instigated by those who, by the aid of other prime mo- 
vers, were unable to compete with the improved agency of 
steam. The experiment, however, was so far successful, as 
to satisfy all that the engine might be advantageously adapted 
to almost every species of manufacturing industry. 



224 CARTWRiCHT— SADLER. 

In 1785 the first cotton mill moved by steam was erected by 
Messrs. Robinson and Papplewick, in Nottinghamshire. In 
1788, a coining apparatus for copper was erected at Soho, and 
driven by a steam engine ; the machinery there applied has 
been imitated at the Royal Mint of Great Britain and the Impe- 
rial Mint at St. Petersburgh, and all were set in motion by dou- 
ble-acting engines on Watt's construction. 

In 1793, cotton was first spun at Glasgow by steam. In the 
year 1793, it was introduced into the woollen, worsted, and flax 
manufactures ; and in 1797 was employed at Sheffield for 
grinding cutlery. 

179. In the year 1800, the extended term of Watt's patent ex- 
pired. Up to this time the introduction of his engine into use 
had been slow. This has been ascribed to the prejudice enter- 
tained against the monopoly, but probably is in some measure 
due to the fact that the arts did not keep up with the rapid im- 
provement of the steam engine. At this date the steam engines 
in London did not exceed 650 horse powers ; in Manchester, 
450 were in use ; and about 300 at Leeds ; while upon our own 
continent but four engines of any importance were to be found, 
two of them at Philadelphia and one at New-York, all employ- 
ed for raising water. 

180. During the continuance of Watt's patent, various plans 
were proposed, which were rendered abortive in consequence 
of his being in possession of the sole right of using the only plan 
by which low pressure engines could be rendered efficient, the 
separate condenser. Hence, with the exception of Hornblower, 
against whom Watt and Bolton obtained a verdict, there are no 
important names to be mentioned, except those of Cartwright 
and Sadler ; these two engines are chiefly remarkable for the 
suppression of the lever-beam. 

Watt, as we have already stated, proceeded in his improve- 
ments slowly and gradually, and they were all applied to the 
form in which he found the engine existing. Hence the beam, 
a heavy and cumbrous appendage, formed a constant part of 
all his engines, as it had done of the original pumping engine of 



CART WRIGHT SADLER. 225 

Newcomen. The parallel motion, the connecting-rod, the sun 
and planet wheel, the rods of his air, cold, and hot water pumps, 
were all adapted to this part of the ancient apparatus ; and from 
the use made of it in working the latter, it appeared to be almost 
indispensable. In Cartwright's engine the beam was suppress- 
ed altogether, and with it the separate pumps. A cross-head 
was placed upon the piston-rod, bearing two short connecting 
rods, that turned the cranks of two wheels of equal diameter 
catching into each other, and a pinion attached to the axis of 
the crank was driven by one of them. As this engine did not 
work as well as the double-acting engine of Watt, it merits no 
further notice at this stage of the history ; although, had it ap- 
peared before the improvements of Watt, it would have been 
of great value. Cartwright is, however, to be mentioned with 
high praise as the inventor of the metallic packing for pistons, 
which, as has been stated on a former page, promises to super- 
sede all others. 

Sadler's engine was a single-acting engine, differing from 
Watt's principally in the position of the equilibrium valve, 
which was situated in the piston itself. A wheel was fixed to 
an axis passing at right angles through the top of the piston- 
rod ; this worked between guides, and on the opposite end of 
the axis was placed the connecting-rod that turned the crank 
of the fly-wheel. The rod of the air-pump was worked by a 
short lever, the centre of whose motion was at the end, instead of 
the middle, as in the ancient beam, and which, having no other 
work to do but that of pumping, was much lighter than the latter. 

From the date of the expiration of Watt's patent, the use of 
the double-acting condensing engine has been extended in a 
rapidly increasing ratio, insomuch that far more engines are 
now made at Soho, in spite of the ardent competition of various 
manufacturers, than were ordered while Watt was possessed of 
the sole right of making engines, as well as using his principle. 

181. The improvements made in the condensing engine since 
that period have principally consisted in the finish and perfec- 
tion of the parts, and in this Murray of Leeds has been most 
distinguished, his engines having a beauty of proportion and 

29 



226 MURRAY — WOOLFE. 

accuracy of workmanship exceeding most others. In England, 
the beam has been continued in almost all cases except in the en- 
gine of Maudslay, while in this country it has, in many instances, 
been laid aside. The first engines constructed in America for 
Fulton's steam-boats have the form represented in PI. VII., 
which is superior to that of either Sadler or Maudslay. Where 
the beam is retained, the parallel motion has been superseded, 
in several American engines, by a simple slide to guide the con- 
necting strap. The adaptation of this to the lever beam is the 
invention of Mr. R. L. Stevens, whose name we shall have occa- 
sion to quote hereafter as a successful constructor of steam-boats. 
The eccentric and slide valve belong to this last period of 
the history of the double-acting engine, but their invention has 
been already referred to. 

182. The use of the expansion of steam has been stated to 
have originated with Watt, and we have mentioned the attempt 
of Hornblower to adapt the same principle to an engine com- 
posed of two Cylinders. This, which was defeated in conse- 
quence of its interfering with Watt's patent, was revived in 
1804 by Woolfe, with a boiler for generating high steam. This 
engine has been found to work to great advantage ; but for 
reasons mentioned in speaking of Hornblower's engine, it will 
be obvious that steam of equal tension would act to still greater 
advantage in an engine composed of but a single Cylinder. 
This last method has received great extension in several Amer- 
ican engines, and in the pumping engines of Cornwall. 

It has been seen that the plans proposed during the term of 
Watt's patent were either such direct infringements as to be 
prohibited by legal proceedings, or wholly inferior in utility to 
his inventions. The very year, however, that saw his patent 
expire, also saw the introduction into use of two engines, that, 
had they been brought into perfection before, might have com- 
peted with that of Watt upon equal terms. For the history of 
one of these we are compelled to go back almost to the date of 
Watt's earlier discoveries. ' 

183. Oliver Evans, well known in this country as an excel- 



EVANS. 227 

lent mill -wright, and as the inventor of the labour-saving ma- 
chinery in grist mills, entertained the idea of the possibility of 
propelling wagons by the action of high steam as early as 1772. 
Soon after, he ascertained, by experiment upon a small scale, 
the practicability of so doing ; and in 1786 applied to the State 
of Pennsylvania, which (under the old Confederation) had not 
parted with this attribute of sovereignty, for an exclusive privi- 
lege. It is well to remark that his engine was from the first 
intended to be double-acting, and that even the last-mentioned 
date is but little later than the construction of the engines for 
the Albion mills, whose principle was long kept secret by Watt. 
His applications, both for private and public patronage, were 
treated as the reveries of insanity, and it was not until 1801 
that success in his profession enabled him to raise the funds for 
erecting an experimental engine. This was first applied to 
grind gypsum, and afterwards used in sawing marble. It was 
publicly exhibited in Philadelphia in that year. 

In 1804 he was employed by the corporation of Philadel- 
phia to construct a dredging machine to be worked by steam ; 
with this he made successful experiments, both on locomotion 
and navigation by steam s that will be mentioned in their proper 
place. Not the least of the improvements of Evans lies in the 
form of his boilers, which he was the first to make in the form 
of a cylinder ; a form that we have already shown to be prefer- 
able to any other yet proposed. His first experiments were made 
with a gun barrel, and he steadily adhered to that form in his 
subsequent operations. 

The engine of Evans retained the lever beam of Newcomen, 
and has been copied in this respect in many American engines, 
of which the beautiful one figured on PI. V., is a specimen. In 
others, the arrangement in PL VII. has been adopted, and others 
again are horizontal, as represented on PI. VI. The latter 
form has hitherto been principally used on the Mississippi and 
its branches. The high pressure engine came more early into 
general use in the United States than it did in Europe, and 
long experience has rendered its proportions better understood 
in our country than they are in England. It is with us the 
favourite form, except in the steam-boats of the Atlantic coast. 
In these, a fear of the greater danger, with which it was thought 



228 WATT. 

to be attended, has prevented its introduction. It seems, how- 
ever, to be now almost conceded, that, with proper precautions, 
boilers generating 1 high steam may be rendered as safe as any 
others ; and hence the conclusion has been drawn that high 
steam, acting expansively, as it is the most powerful application 
of steam, will, wherever circumstances will admit, supersede 
all other methods. 

184. The year 1801 also witnessed the construction of the 
high pressure engine of Trevithick and Yivian. The boiler in 
this case was a Cylinder of cast iron ; the fire was made within 
it, and hence it is less safe than the boiler of Evans. The Cy- 
linder was immersed in the boiler, in order to retain the heat 
of the steam. In the first engines it was attempted to condense 
the steam ; but this is always attended with disadvantage, un- 
less when the steam has had an opportunity of cooling itself by 
expansion. The fly-wheel, connecting rod, and crank were 
above the Cylinder, and no parallel motion or beam was need- 
ed. In the application of the engine to locomotion, a plan of 
connecting rods like those on PI. VII. was finally adopted, but, 
so far as we can learn, only one connecting rod was used at first, 
even in this case, as in the engines of Sadler and Maudslay. 

Such is the history of the engines that are now in actual use, 
or have served as steps to the present state of the art. Another 
class remains to be mentioned. 

185. Watt had included in his first patent a method of pro- 
ducing a rotary motion by the direct action of steam, but had 
with sound judgment abandoned it in favour of a double-acting 
Cylinder engine. In spite of this virtual acknowledgment of 
the inferiority of this principle, innumerable projects have since 
been entertained of rotary engines. The result of these exper- 
iments may be summed up in a few words. The advantage to 
be derived is, in fact, of but little moment, while the mechanical 
difficulties that lie in the way are such as have hitherto prevent- 
ed any engine having a rotary motion, produced by the direct 
action of steam, from coming into general use. 

Among the various rotary engines which have been proposed, 
we may mention one by the Hon. R. Sherman of Connecticut, 



ROTARY ENGINES. 



229 



which was exhibited recently in New- York, and which per- 
formed well. 

That which is exhibited in the annexed draught, has been 

Fig: 1. 




Fig. 2. 




230 WATT. 

for several years in actual use in the western part of the state 
of New- York, and has been employed to propel a boat on the 
Morris Canal. In this engine the gates marked 1 and 1 receive 
the pressure of the steam which enters through the passage 5, 
and is discharged at 6. These passages are so situated that 
one of the gates will be always receiving the pressure, and dur- 
ing its action the other gate is lifted over a partition or diaphragm 
by means of a curved wheel 7, which runs between friction 
rollers. Of this engine Fig. 1. is a section, and Fig. 2. a plan. 

The principle of reaction, which has been attempted in Bar- 
ker's mill, where water produces a rotary motion by issuing from 
holes placed near the ends of a moveable arc, has also been pro- 
posed as a mode of using steam. We have described an in- 
stance of this kind in the engine of Avery. 

The Cylinders of engines have occasionally been suspended 
on trunnions; in this case the piston-rod may be applied directly 
to the crank. The earliest of these was one constructed by 
French in 1808, in a steam-boat in the Harbour of New- York, 
a model of which of the same date is among the apparatus of 
Columbia College. 

186. In the brief sketch we have thus given of the History 
of the Steam Engine, many ingenious contrivances and inven- 
tions have been passed over. These have been omitted for want 
of space, and because few of them, however ingenious, have had 
any prominent effect in introducing the steam engine into more 
general use. The different forms of boilers that have been pro- 
posed, or even actually used, would occupy no small room. The 
object of our essay is, however, accomplished when the engine 
has been traced, from its first rude beginning to those forms in 
which it is found in most common use, and when we have notic- 
ed those different inventions that have tended to facilitate its pro- 
gress, or by which it has been fitted the better to subserve the pur- 
poses for which it was invented. The most important step is un- 
doubtedly that made by Watt, and it is remarkable in the history 
of the arts, not more from the immense value that it has had in 
its practical application, than for being the result of scientific 
research and the study of physical principles, by the most ele- 
gant and accurate processes of induction. 



CHAPTER IX. 

APPLICATIONS OF THE STEAM ENGINE. 

General view of the applications of the Steam Engine. — Rais- 
ing water. — Grinding com. — Cotton Spinning. — Naviga- 
tion. — Bossufs laws of the impact of fluids. — Principles of 
the action of Paddles. — Juaids laws of the action of fluids 
on solids moving in them. — Maximum speed of vessels. — 
Poioer required to propel paddles. — Relation between the 
power and the surface of the Paddles. — Laivs of the motion 
of Steam-boats. — Theory of paddle wheels. — Comparison 
behoeen theory and observation. — Practical Rules. — Sug- 
gestions for the improvement of Steam Navigation. — 
Steam-boat engines. — History of Steam Navigatioti. — Na- 
vigation of the Ocean by Steam. — Rules for Boilers of 
Steam-boats. — Application of Steam to Locomotion.- — His- 
tory of the Steam carriage. — Conclusion. 

187. The steam engine is now applied to almost every spe- 
cies of manufacturing industry, and as a substitute for the la- 
bour of men and animals in almost every art, and in many of 
the other cases in which they were formerly employed. In its 
earliest forms it was used to raise water, and still in its more 
perfect shapes fulfils the same object ; it performs almost every 
variety of manufacturing manipulation ; propels vessels through 
the water ; and drags carriages upon railways, and even upon 
common roads. 

188. In raising water, pumps may be adapted to the beam of 
the engine, and the useful effect may be safely taken, at the 
raising of 240001bs, one foot high per minute, for every horse 



232 STEAM-BOATS 

power of the engine, estimated in the manner that has been 
pointed out. 

In pumping by the steam engine, it would appear from ex- 
perience that the stroke of the pump-rod should not exceed 
eight feet. The number of cubic feet of water which a pump 
will deliver per minute, may be found by multiplying together 
half the velocity of the pump-rod, the square of the diameter 
of the barrel, and the constant fraction 0.00518. The velo- 
city at which the maximum work is performed, and which is to 
be used in the foregoing calculation, is found by multiplying 
the square root of the length of stroke by the constant number 
98. The proper velocity for a pump of 8 feet stroke is there- 
fore about 270 feet per minute, and as the pump-rod is suspend- 
ed from the end of a lever of equal arms, the velocity of the 
piston of the engine is the same. 

The friction of the pumps is estimated as equal to a column 
of water whose height is the sum of 1^ feet for each separate 
pump or lift, and of r^th of the whole height to which the water 
is to be raised. These quantities must be added, therefore, to 
the height, in order to obtain the efficient resistance. Calling this 
H ; the number of cubic feet of water to be raised per minute, 
W ; the pressure of the steam on each circular inch p • and as- 
suming the velocity of the piston to be 180ft : D, the diameter 
of the cylinder of the steam engine is found by the formula, 

'HXWX0.7332> 

The diameter of the barrel of the pump may be found by the 
formula,* 

d=V3.15W 

These rules are independent of the conventional estimate of 
horse power, and are therefore well adapted to practical appli- 
cation. 

The estimate of the quantity raised per horse power, which 
has been given above, has been far exceeded in practice by the 
expansive action of steam. The duty of the pumping engines 
in Cornwall has been raised in this way from an average of 17 

* Grier's Dictionary. 



D=V ( HXWX0.733 2) 



STEAM-BOATS. 233 

millions of pounds for each bushel of coals to one of 43£ mil- 
lions, and one engine has raised more than 90 millions. 

189. In Grist mills, it is estimated that the power of five horses 
is necessary for every run of stones, and for performing the 
work necessary to supply them, moving the whole of the usual 
labour-saving machinery. In applying the engine to this pur- 
pose, rotary motions of the proper velocity are taken off from 
the axis of the crank by systems of wheels and pinions. 

The dimensions of engines to perform this description of 
work are given in the following table :* 



Bushels Ground 
per hour. 


Diameter of Cylinder 
in inches. 


Bushels Ground 
per hour. 


Diameter of Cylinder 
in inches. 


4 


12.5 


26 


29 


e 


14.6 


28 


29.8 


8 


16.75 


30 


31.1 


10 


18.5 


32 


32 


12 


20.2 


34 


33.3 


14 


21.75 


36 


34.2 


16 


23.25 


38 


35.2 


IS 


24.75 


40 


36 


20 


26.25 


42 


37.3 


22 


27.25 


44 


38 


24 


28.1 


4S 


39.5 



The engine is supposed to be double-acting, condensing, and 
using steam without expansion. By employing the expansive 
action of the steam, an increase in the quantity of work which 
may be performed will be obtained, in ratios which may be 
inferred from our previous investigation of that method of 
action. 

190. In manufacturing machinery, the motions are taken off 
in the same manner. It would be tedious, nay impossible, to 
recite every particular case of this sort ; we shall therefore limit 
ourselves to the spinning of cotton. In this branch of manufac- 
ture, it is estimated that each horse power will drive 200 thros- 

*Grier's Dictionary. 

30 



234 STEAM-BOATS. 

tie spindles, or 1000 mule spindles, and perform all the work 
of preparing the cotton for them. 

Those subjects which appear to require more full illustra- 
tion in this work, are the propulsion of vessels, and the motion 
of carriages upon rail-roads. 

191. Vessels in which steam is used as the moving power, 
are generally propelled by the action of paddle wheels. These 
receive a continuous rotary motion from the steam engine, and 
the paddles tend to impel the vessel in consequence of the re- 
sistance which opposes their passage through the water. This 
method, which is the most simple and perhaps the most obvious, 
has in practice been found preferable to any other which has yet 
been proposed. In order to give motion to a paddle-wheel, it is 
only necessary that it should be fastened to the axle of the 
crank of any of the usual forms of engine. The wheel will 
thus be caused to perform a complete revolution in the same 
time that the piston takes to perform a stroke, estimating un- 
der that term its whole motion, from the time it leaves either ex- 
tremity of the cylinder, until it return again to the place whence 
it set out. 

The force which the wheels exert in propelling the vessel 
depends upon : the velocity with which they strike and move 
through the water ; the immersed area of the paddle ; and the 
fluid resistance of the water. The velocity of the vessel will 
depend upon the force with which the wheel tends to impel it 
on the one hand, and the resistance the water opposes to its 
progressive motion on the other. 

To determine the velocity a given engine will give to a vessel, 
and the conditions under which a maximum effect may be 
produced, is evidently a problem of great complexity. It does 
not appear yet to have been solved in a satisfactory manner, 
nor does it seem to be within the strict limits of analysis, in con- 
sequence of the great number of circumstances which must be 
taken into account. It is, however, possible, by reference to 
scientific principles, and comparing their results with the facts 
observed in practice, to form rules which may be of value in 
the construction of steam vessels. 



NAVIGATION BY STEAM. 235 

The action of a pacldle-wheel upon the water must be gov- 
erned nearly, if not exactly, by the laws which fluids follow in 
impinging upon solid bodies. These may be stated as fol- 
lows : 

1. With equal surfaces equally inclined to the fluid, the re- 
sistances are nearly proportioned to the squares of the veloci- 
ties ; 

2. With equal velocities, and equal inclinations of the sur- 
faces to the fluid, the resistances are proportioned to the areas of 
the surfaces ; 

3. With equal velocities and equal surfaces, the resistances 
are nearly proportioned to the squares of the angles of inclina- 
tion, until the angle of incidence diminish to 50° ; beyond this, 
the resistance decreases more rapidly. 

4. The measure of the action of a fluid upon a plane surface, 
to which it acts at right angles, is equal to the weight of a co- 
lumn of the fluid whose height is that whence a heavy body 
must fall to acquire the velocity, and whose base is the area of 
the surface on which the fluid acts. 

5. As the resistance increases in the ratio of the squares of 
the velocities, there must be a maximum beyond which a given 
force cannot propel a plane surface through a fluid. 

6. This maximum velocity being given, the maximum of 
effect will be produced by a paddle-wheel when it moves 
through the water with one third of that maximum velocity. 

192. Experiments appear to be wholly wanting by which 
the maximum velocity of a plane surface, moving through a 
fluid, can be determined. It, however, happens that this may be 
deduced from observation of the rate at which the wheels of 
steam vessels move ; for there is in most cases a very consider- 
able excess of power, and hence the relative velocity of the 
wheel necessarily becomes that at which the work is most 
efficiently done, and is therefore one third of the maximum ve- 
locity with which the paddle might be impelled had it no work 
to perform. This relative velocity of the circumference of the 
paddle-wheel has been found in American steam vessels to be 
not far from 6£ feet per second. 



236 NAVIGATION BY STEAM. 

The maximum velocity of a paddle-wheel when it has no 
work to perform, might therefore be takejti at 19£ feet per second, 
or 13.2 English miles per hour. 

Were the laws of the resistance of fluids to boilers moving 
through them identical with those of impact, it might be infer- 
red that the last-named velocity is also that of the maximum 
speed of steam vessels. If we were to take this as the limit, 
it might be inferred that the proper velocity to be given by the 
engine to the circumference of a paddle-wheel should be 26 
feet per second in order to give to the vessel a velocity of 13.2 
English miles per hour, and retain for the wheel a relative 
velocity or rate of motion through the water of 6^ feet per se- 
cond. 

Although this is by no means true, and although there are 
now many instances in which boats have been driven at a 
higher velocity than 13.2 miles per hour. We shall rest at 
this point for the present. 

193. The greatest speed of vessels, and consequently the 
maximum velocity of paddle-wheels, may be examined, either 
by the aid of theory, or ascertained by actual experiment. For 
the theoretic investigation we may have recourse to the princi- 
ples of Don George Juan. 

It is stated by this author, that the resistance which opposes 
the motion of bodies moving in fluids, may be divided into 
three parts : — 

1. A resistance growing out of the disturbance of the condi- 
tions of equilibrium, and arising from the friction of the fluid. 
This is a constant force. 

2. The fluid resistance proper, which varies with the square 
of the velocities. This has so small a co-efficient, that it is in- 
sensible at small velocities, but increasing with their squares, 
it speedily becomes the most important, and the first bears then 
so small a relation to it, that at mean velocities this need alone 
be taken into view. 

3. The wave raised in front of the moving body, and a want 
of support from behind, growing out of the space which the 
body leaves unfilled behind it when the velocity becomes 



NAVIGATION BY STEAM. 237 

great. The mere resistance, growing out of these causes, in- 
creases with the fourth power of the velocities, but, in addition, 
the weight of the body must be raised upon an inclined plane, 
and hence will arise a limit beyond which the velocity of a ves- 
sel cannot be carried. 

At small and mean velocities, this species of resistance is 
wholly insensible, but it finally becomes, in consquence of its 
rapid increase, the most important of the three. It is when this 
occurs that we would fix the limit of the speed that can be ad- 
vantageously given to a vessel, or with which a paddle can be 
impelled. 

194. The exact limit of speed at which the wave raised in 
front of a vessel becomes an insuperable obstacle to an increase 
of velocity, depends upon circumstances for which no theory 
can account. In our former edition we ventured to place this 
limit at 12 nautical miles per hour, and this was the greatest 
speed which had been reached in American steam-boats. In 
all which then existed, a prodigious wave was raised in front 
at rapid motions. This important resistance led our naval 
architects to modify the figure of the prows, and they have 
thus proceeded by successive steps, until, in the case of the 
steam-boat New- York, no perceptible wave is formed. It ap- 
pears, therefore, almost impossible in the present state of our 
knowledge to limit the speed which may be attained by steam- 
boats. 

The experiments of Juan were made at velocities less than 
the least which are now given to steam-boats, and there is good 
reason to believe that his theory ceases to be true at the higher 
velocities. The result of the practice upon the Hudson seems 
to prove, that at velocities exceeding 10 nautical miles per hour, 
the resistance, so far from varying with the squares of the velo- 
locity, becomes almost constant. This at least is certain : every 
increase in the rotary velocity of the paddle-wheel, has been at- 
tended with an equal increase in the progressive velocity of the 
vessel. The expenditure of steam is, however, in a greater ra- 
tio than the velocity ; but this is easily accounted for when it is 
considered that, in order that it exert a given pressure on a pis- 



238 NAVIGATION BY STEAM. 

ton in more rapid motion, it must have a greater tension in the 
boiler. 

Experiments have been made on a large scale upon the mo- 
tion of boats on the Firth and Clyde, and on the Monkland 
Canal in Scotland, by Mr. McNeill. His conclusions as are fol- 
lows : 

1. In a wide and deep canal the -resistance was observed to 
increase with the velocity, but not in any uniform ratio. 

2. In a shallow and narrow canal the resistance had a limit 
at a certain velocity, and thereafter decreased with an increase 
of the velocity. 

3. That the resistance bore a relation to the inclination of the 
keel. 

4. That the boat rises in rapid motion, being in some cases, 
on an average, four inches less immersed in the water than 
when at rest. This rise was greatest at the bow, and least at the 
stern. 

Mr. Russell, who had observed similar facts, comes to the 
conclusion that at a velocity of 43.8 miles per hour the vessel 
would no longer be immersed, but would skim along the sur- 
face. This corresponds with what is observed in the ricochet 
of cannon balls, which occurs only so long as they retain con- 
siderable velocities. 

195. To determine the power required to propel a paddle- 
wheel through the water with a given velocity, we must consi- 
der that the measure of force depends not only on the resistance 
overcome, but the velocity with which it is conquered. Hence 
it would appear that the resistance estimated as being equal to 
the weight of a column of water whose base is the area of the 
paddle, and whose height is that whence a heavy body must 
fall to acquire the velocity, is to be multiplied by the velocity 
per minute, and the product divided by the weight raised by the 
unit of power in the same space of time. 

The height due to a given velocity is found by dividing the 
square of the velocity per second by the constant number 64. 

The unit of power is 32,0001bs. raised one foot high, but 
this is probably reduced in the machine itself, as we have here- 



NAVIGATION BY STEAM. 239 

tofore seen, to 24,0001bs. Hence we would have the following 
rule : 

Multiply together the cube of the relative velocity, the num- 
ber of seconds in a minute, the weight of a cubic foot of water 
in 62^-lbs., and the area of the paddle in feet, divide the pro- 
duct by the constant number 24,000 multiplied by the constant 
number 64, the quotient is the horse power. 

This rule, however, is obtained by neglecting very many of 
the circumstances which ought to be taken into account, and 
must therefore be very wide of the truth. It is also difficult to 
determine the mean relative velocity, for this varies at every 
possible inclination of the paddle. A very beautiful investiga- 
tion is given in one of the appendices to the new edition of 
" Tredgold on the Steam Engine," by Mr. Morway. In this, all 
the circumstances seem to betaken into account, and the results 
of the theories correspond very closely with observation in 
British steamers. We fear that this elegant investigation gives 
formulas altogether too complex for the use of practical men. 
We shall, in consequence, prefer to deduce rules from experience. 

The other rules, which have been deduced from theory, are 
as follows : 

In the same vessel, and with a constant relation between the 
area of the paddle-wheels and the transverse section of the 
vessel, the velocities are as the cube roots of the powers of the 
engines. 

The relation between the velocity of the wheels and of the 
vessel is constant so long as the ratio between their surfaces 
remains the same. 

It is obvious that this last rule cannot be correct, if it be true, 
as we have inferred, and shall hereafter show by a comparison 
of various observations, that the relative velocity of the circum- 
ference of paddle-wheels is a constant quantity. 

196. If we apply the rule for the area of paddle-wheels to the 
case of a paddle-wheel working at a maximum, or with a rela- 
tive velocity for its vertical paddle of 6.5 feet per second, we 
shall find that each horsepower of the engine should be capable 
of impelling a paddle of half a square foot. But a paddle does 



240 NAVIGATION J?Y STEAM. 

not act during the time of its immersion in the water with equal 
intensity ; and although no loss of power might arise from this 
cause, the obliquity of its action applies a part of the force to 
resistances that do not assist in propelling the vessel. Thus, 
on entering the water, a part of the force is applied to lift the 
wheel from its axis, and on quitting the water to press it down. 
In addition, a quantity of water is raised upon the paddle, apart 
of whose weight acts in direct opposition to the moving power. 
The loss growing out of these causes can only be investigated 
experimentally. We shall attempt this from a comparison of 
the circumstances of the steam-boats North-America and Presi- 
dent. The former navigates the Hudson River, and is remark- 
able for a speed that has hitherto never been equalled by any 
other steam vessel ; the latter plying between New-York and 
Providence, it has been found, in her construction, necessary to 
preserve stability as well as to obtain speed, and if her velocity 
be less than that of the former, she still combines the two quali- 
ties of speed and safety in a degree superior to any vessel we 
are acquainted with. 

The particulars necessary for our purpose in relation to the 
President, are as follows, viz : 

Breadth of beam, . . . . . 32 ft. 6 in. 

Draught of water, 9 ft. 

Diameter of Water-wheels, . . 22 ft. 

Length of bucket, . . . . . 10 ft. 

Depth of do 3 ft. 6 in. 

She has two engines of the following dimensions : 

Diameter of Cylinder, .... 4 ft. 

Length of Stroke, 7 ft. 

Number of double strokes or complete revolutions of paddle- 
wheel per minute, 21 . When but one engine works, the number 
of revolutions of the single wheel on which it acts are reduced 
to 17£. 

The average passages to Providence have been performed, 
when both engines acted, in 15£ hours ; when but one was 
used, in 19£. 

The distance between New- York and Providence is usually 
estimated at 210 miles ; carefully measured, however, upon a 



NAVIGATION BY STEAM. 241 

map, it is found to amount to no more than 160 nautical, or 
184.3 English miles. From these data, the average velocity 
of the boat through the water is very nearly 12 miles per 
hour, or 17.6 feet per second ; the average relative velocity of the 
wheel 6.5 feet per second, when both wheels and engines were 
in motion ; the average velocity of the boat when but one en- 
gine worked, becomes 9.45 miles per hour, or 13.86 feet per 
second ; the relative velocity of the wheel 6.3 feet per second. 
The wheels, therefore, move with a relative velocity almost 
identical with that which our hypothesis has assumed to cor- 
respond to a maximum effect. But the actual effect is far be- 
neath the rule we have laid down. Estimated from a compa- 
rison with other condensing engines, those of the President 
would have each a nominal power of about 110 horses, which, 
in consequence of the rapidity of their action, is increased to 
about double ; but by the rules on page 121, the power of each 
of the engines is that of 160 horses. As each paddle has a 
surface of no more than 35 square feet, each horse power drives 
no more than 0.22 feet of paddle, or less than one-fourth of a 
square foot. And it would appear, from comparing the relative 
velocities in these two cases, as if, in this vessel, the proper 
ratio between the moving power and the paddle had been at- 
tained. 

The North-America has the following dimensions : 

Breadth of beam, 30 ft. 

Draught of water, 5 ft. 

Diameter of Water-wheel, -:-_•- 21 ft. 
Length of bucket, ------ 13 ft. 

Depth of do. 2 ft. 6 in. 

She has two engines of the following dimensions: 
Diameter of Cylinder, - 44£ in. 

Length of Stroke, - - - • - - 8 ft. 
Double Strokes per minute, 24. 
The estimate of her speed furnished by her owners, is 19.8 
feet per second. The relative velocity of the wheel is 6.6 feet 
per second, exceeding our theoretic limit one-tenth of a foot. 
The relation between the velocities of the boat and the wheel 
is as 3 to 4. 

31 



242 NAVIGATION BY STEAM. 

The power of each of the engines, estimated by the rule on 
page 121 , is 186 horses, the area of each paddle 32^ ; and hence 
each horse power propels no more than 16 hundredth parts of 
a square foot through the water. 

The velocity of the wheel is, however, greater than that of 
the President in the ratio of 6.3 : 6.6, or of 21 to 22 ; which 
makes the comparison more favourable than would at first ap- 
pear, to the North-America. For, conceiving the wheel of the 
former to work to the greatest possible advantage, each horse 
power would, at the increased relative velocity the latter has, 
propel no more than one-fifth of a square foot of paddle. 

The powers of the engines of both boats, as estimated by us, 
far exceed what would usually be ascribed to them from a 
mere consideration of their dimensions. Those of the President 
being of the size of condensing engines usually estimated at 
110 horse powers ; those of the North-America, at 98 horse 
powers. This difference arises from the great speed with which 
they are driven ; it being usual to give no more velocity to the 
piston of a condensing engine than about 200 feet per minute, 
while that of the North -America has 3S4 feet, and that of the 
President 336 feet. 

The near coincidence of the actual performance of these 
boats with our theory, except in one respect, is a tolerable 
warrant for its accuracy. The point in which this difference 
occurs, is the area of paddle that can be driven by each horse 
power of engine. The rule on page 239 would make this force 
equivalent to move half a square foot with the velocity of 6.5 
feet per second ; while in the case of the President, the actual 
performance, reduced to that velocity, is no more than one-fifth 
of a square foot ; while in the case of the North-America it 
falls as low as one-sixth. The disturbing causes that effect this 
variation from the theory are obvious, and have been explained, 
but it is not easy to reduce them to calculation. 

In the new class of vessels which has come into use in the 
neighborhood of New- York similar results have been obtain- 
ed, as will appear from the following facts : 



NAVIGATION BY STEAM. 243 

Steam-boat Cleopatra. 

Diameter of wheel, - 23 ft. 

Length of bucket, - - - - ll£ft« 

Breadth of do. 2fft. 

Revolutions per minute, 24 

Velocity of wheel per second, - - 28.8 ft. 

of vessel, ----- 22.6 

Relative velocity of wheel, - - - 6.2 

Steam-boat Lexington. 

Diameter of wheel, - - - - 24 ft. 

Length of bucket, - - - - lift. 

Breadth of do. 2|ft. 

Revolutions per minute, - - - 23 

Velocity of wheel per second, - - 28.8 ft. 

of vessel, - 22.5 ft. 

Relative velocity of wheel, 6.3 ft. 

Steam-boat Massachusetts. 

Diameter of wheel, - - - - 22 ft. 

Length of bucket, - - - - 10 ft. 

Breadth of do, ----- 2^ ft. 

Revolutions per minute, 26 

Velocity of vessel per second, - - 19.95 ft. 

of wheel, - 26.25 ft. 

Relative velocity of wheel, - 6.3 ft. 

The same general fact, that the velocity of a paddle-wheel 
through the water is a constant quantity in a wheel of given 
diameter and dip, and does not vary in different wheels materi- 
ally from 6.3' ft. per second, has been observed in the high pres- 
sure steam-boats which navigate the Mississippi and its branch- 
es by Professor Locke, 

197. We have seen that, according to the usual theory, the 
resistance sustained by a body moving in a fluid is proportion- 
ed to the square of its velocity and the area of its section. 

The moving force, necessary to give a vessel a given velo- 



244 NAVIGATION BY STEAM. 

city, should therefore, as has also been stated, be equal to this 
resistance multiplied by the velocity, or proportioned to the 
cube of the velocity; and in similar vessels the resistance is 
proportioned to the square of one of the homologous dimen- 
sions. 

Thus, to obtain double the velocity in a given vessel, and 
with given wheels, it might appear eight times the force should 
be employed, and so on. 

But, as the space passed over in a given time is proportioned 
to the velocity, the actual expenditure of power, in performing 
a given distance, is proportioned to the squares of the veloci- 
ties. 

These laws would be true only when the weight of the en- 
gine is considered as constant, but as this increases in a greater 
ratio than the power, it would make the acquisition of great ve- 
locities still less advantageous. 

If, however, we have recourse to facts instead of theory, we 
find that the resistance never increases in the cases which occur 
in practice, in a ratio as great as the square of the velocity ; and 
it appears probable, that at the higher velocities it becomes al- 
most constant. Supposing the resistance to vary with the ve- 
locity simply, we obtain the following rules, which are more con- 
sistent with experience : 

(1). To obtain double the velocity in a given vessel, we must 
employ an engine of 4 times the power. 

(2). To obtain an equal velocity in similar vessels of differ- 
ent dimensions, we must employ engines varying in force toith 
the areas of their transverse sections, or toith the squares of 
their homologous lineal dimensions ; or, to express the same 
fact in another manner, with the squares of the cube roots of 
their respective tonnages. 

(3). The actual expenditure of power in passing through a 
distance with different velocities is as the velocities. 

An obvious advantage will be gained by increasing the size 
of the vessels^ for the resistances vary as the square of similar 
dimensions, while the tonnage increases with their cubes. 

It has been imagined by some, that the motion of steam-boats 
was different in a current from what it is in still water. This, 



NAVIGATION BY STEAM. 245 

however, cannot be the case, unless it be so rapid that the slope 
becomes an important element, forming an inclined plane up 
which the weight is to be lifted. This conclusion is obvious 
from the following considerations. When a vessel is in a cur- 
rent, and the propelling force ceases to act, she speedily acquires 
the velocity of the fluid, and is relatively at rest in respect to it. 
If the propelling force be steam applied to wheels, and they be 
set in motion, the action upon the fluid is precisely the same as 
if no current existed, and hence the velocity through the water 
will be the same as when the fluid is at rest. Thus, then, the ve- 
locity, in respect to the shore, will be the sum or difference of 
the velocity the vessel would have in still water, and that of 
the stream. The case is, of course, widely different when the force 
is applied by chains, or other connexion, with a fixed point up- 
on the shore. 

198. The next consideration in respect to paddle-wheels is 
their diameter. This is determined by means of the velocity 
that it is intended to give the circumference, compared with the 
velocity of the piston ; the wheel being attached to the crank will 
make half a revolution for each stroke of the piston. Hence, in 
this mode of gearing the wheels, great velocities can only be at- 
tained by a proportionate increase of the diameters. This is at- 
tended with several practical inconveniences, first in a great in- 
crease of the weight, and secondly in raising the height of the 
centre of gravity. The action of a paddle depends, as has been 
shown, upon its relative velocity, but when the paddles of a 
wheel act in succession, the water will follow in the wake of 
the first which acts ; and the second may, if it succeed at too 
short an interval, impinge upon water that is already in motion. 
For this cause, the paddles upon the wheels should not be more 
numerous than is just sufficient to keep up a continuous action. 
The proper arrangement, for this reason, is such, that when 
one paddle is vertical, the preceding one shall be just issuing 
from, and the succeeding one just entering the water. 

When paddle-wheels impinge against the water in an oblique 
direction, they sustain a sudden shock, when the interval is as 
great as we have pointed out ; the reaction of this sudden re- 



246 NAVIGATION BY STEAM. 

sistance upon the engine is injurious, and it checks and destroys 
the accumulation of power which the water-wheel might other- 
wise attain, and distribute, upon the principle of the fly-wheel. 
Hence in the early steamboats, fly-wheels driven with greater 
velocity than the paddle-wheels, were found of great value ; 
and even in the rapidly moving boats of the present day, where 
the velocity and weight of the paddle-wheels enable them to 
answer the purpose of a fly-wheel, these shocks are not without 
an injurious effect. 

Various methods have been proposed to remedy this defect. 

In some English steam-boats, the paddles have been placed 
obliquely upon the circumference of the wheel, but still perpen- 
dicular to a plane tangent to it ; their inclination to the vertical 
plane, therefore, remains the same as in the usual form, but 
they enter the water by an angle, instead of striking with one 
side, and hence do not experience the shock of which we have 
spoken. 

There is, however, a defect which more than compensates 
any advantage to be derived from this arrangement. The wheels 
act in directions inclined to the plane of the vessel's keel, and 
thus a part of their power is exerted to press the vessel in a 
lateral direction ; and although the two wheels mutually neu- 
tralize this part of each other's action, the whole of the force 
exerted in this direction is wasted. 

A better arrangement has been introduced into his steam- 
boats by Mr. R. L. Stevens. The wheel is triple, and may be 
described, by supposing a common paddle-wheel to be sawn 
into three parts, in planes perpendicular to its axis. Each of the 
two additional wheels, that are thus formed, is then moved 
back, until their paddles divide the interval of the paddles on 
the original wheel into three equal parts. 

In this form, the shock of each paddle is diminished to one- 
third of what it is in the usual shape of the wheel ; they are 
separated by less intervals of time, and hence approach more 
nearly to a constant resistance; while each paddle, following in 
the wake of those belonging to its own system, strikes upon 
water that has been but little disturbed. 

Believing this oblique action to be a great defect, many at- 



NAVIGATION BY STEAM. 247 

tempts have been made to construct wheels in such manner that 
their paddles might dip and rise from the water in a vertical 
position. The first attempt of this sort was made twenty years 
since by a civil engineer of the name of Busby, who applied his 
wheel to one of the Jersey City ferry-boats. When in action it 
was found inferior in power of propulsion to the common pad- 
dle-wheel, and is, of course, still more so to that of Stevens. 
Within a few years several attempts of the same kind have been 
made in England ; but after impartial investigation by Barlow, it 
seems to be conclusively proved, that, except when there may 
be a great variation in the dip of the paddles, they are inferior to 
the common wheel. 

Still more recently, a paddle to which the name of cycloidal is 
given, has been introduced in England. The form of this may 
be conceived by imagining the paddles of a common wheel to 
be sawn each into three parts by cuts parallel to the axis of the 
wheel, and that two of the parts are each moved backwards one 
third of the distance between two contiguous paddles. This me- 
thod, however is not original, for it was tried some years since on 
the Hudson, and after a fair trial, abandoned. It is unquestionably 
inferior to the wheel of Stevens in river navigation, but possesses 
advantages similar to those with vertical paddles in navigations 
when the dip of the paddle may be subject to variation. This 
variation often occurs in the navigation of the ocean, .as the 
stock of the fuel must be great at setting out, and will be ex- 
hausted before the passage is completed. It cannot, however, be 
questioned that, should it be found practicable to reef the paddles 
of Stevens's wheel in such manner that their dip may be con- 
stant while the draught of water of the vessel changes, this 
method would be superior for the navigation of the ocean to any 
other. 

The objection usually made to the common paddle-wheel, 
and, in consequence, to Stevens's, is, that there is a loss of power 
arising from the oblique action. This loss, it has been shown 
by Barlow, is more than compensated by the increase in the 
relative velocity of the paddle when in its oblique position. It 
thus happens, that with a given expenditure of steam the wheel 
with vertical paddles revolves more rapidly than the common 



248 NAVIGATION BY STEAM. 

wheel, but at the same time gives a less progressive motion to 
the vessel. 

Another loss in the application of the power, arises, as we 
have seen, from the water that is lifted by the paddles as they 
pass out of the water. But the loss is not equal to the whole 
weight lifted, for this water will already have acquired a veloci- 
ty of rotation that will diminish the pressure on the paddle, and 
as the paddle is oblique, the actual pressure may be resolved 
into two forces, one of which retards the motion of the wheel, 
and is lost, while the other acts horizontally to propel the vessel. 
This loss will, of course, be least in large wheels, if the immer- 
sion of the bucket be constant. The larger the wheel, the less 
will be the weight of the water lifted. 

The paddle is not immersed wholly in the water, except when 
nearly in its vertical position. Hence it does not exert a con- 
stant force to propel the vessel, but as the expenditure of power 
from the engine will follow the law of the area, no loss arises 
from this cause. But the inclination of the paddle is, besides, 
constantly varying ; and while the water opposes a resistance 
perpendicular to the surface of the paddle, depending upon the 
area immersed and the square of the velocity ; only that part of 
this resistance, which, when decomposed, is parallel to the surface 
of the water, acts to propel the vessel, the rest is wasted upon the 
vessel, whose weight is alternately lifted and forced downwards. 

A steam vessel is set in motion with a velocity that gradually 
increases until it becomes uniform. At this time the resistance 
of the water to the motion of the wheels exactly balances the 
progressive motion of the vessel. Hence, if we knew the rela- 
tion between the laws by which the resistance to plane surfa- 
ces, and to those of the figure of a vessel, are governed, we 
might determine the proportion which ought to exist between 
the area of the paddle and that of the midship frame of the 
vessel. Experiments by the Society of Arts in London appear 
to show, that when a solid of small size is fashioned into the 
figure of a vessel, the resistance was not more than |th of that 
which opposes a plane surface. Other observations make the 
resistance to good models vary from -^th to i^th. 

But observation on alaro-e scale gives far more favourable re- 



NAVIGATION BY STEAM. 249 

suits. Ill the case we have above quoted of the steam-boat Pre- 
sident, the resistance to the tranverse section of the vessel is no 
more than 2 x th part of that incurred by the wheels when both en- 
gines act ; while, when but one acts, it falls as low as-/- 6 -th. In 
the North -America, it appears to be no more than -^d. This in- 
ference has recently been confirmed by a series of experiments 
recorded in the Transactions of the Royal Society by P. W. 
Barlow. In eleven boats the resistance varied from -^-th to ^th, 
and was at a mean -fc. In the great improvements which ex- 
perience has suggested in the figure of our more modern boats, 
and in the false prows which have been adapted to our older ves- 
sels, the resistance has been diminished still further ; and we need 
no longer hesitate to allow a higher limit than even £ f . The im- 
provements have with sound judgment been directed to the ob- 
ject of preventing the formation of the wave, and thus to get 
rid of the most important retarding cause altogether ; this has in 
some instances been almost completely attained. In the steam 
frigate Fulton, the ratio of these resistances has been reduced 
below -jV. 

The table, therefore, which was given in our first edition, may 
be considered as obsolete. No possible danger, then, can arise, 
in assuming that in a vessel of a good model, the resistance to 
the progressive motion falls as low as-^th part of that which acts 
upon the paddles. If, then, we assume for the relation between 
the absolute velocities of the boat, and the wheel, when work- 
ing to the greatest advantage, the proportion already stated of 
3:4; the most advantageous size of the paddles will be such 
that the area of each should be one-sixth of that of the midship 
frame of the vessel, or the sum of those which act at a time, on 
both wheels, one-third of that quantity. If the engine be so 
constructed as to give the paddle-wheel a rotary velocity of 26 
feet per second, the boat will acquire a velocity of 13.2 miles 
per hour. 

Besides the paddle-wheel, various other plans for propelling 
vessels by steam have been suggested. Some of these will be 
referred to in the history of Steam Navigation. In addition to 
these, it has been proposed to drag vessels by means of a chain 
resting on the bottom of a canal. This method is to be prefer- 

32 



250 NAVIGATION BY STEAM. 

red in this case, inasmuch as the wave which is raised by the 
wheels is destructive to the banks of the canal. This proposal 
has recently been carried into effect with success on a Ferry 
in England. 

In long canals, the expense of a continuous chain is objection- 
able ; but it has recently been discovered that the friction of a 
chain on the bottom of a canal is sufficient to propel a vessel. 
A very ingenious arrangement for this purpose, in which an 
endless chain, of which a part lies on the bed of the canal, and 
is set in motion by a steam engine in the vessel, has been con- 
trived by Mr. Leavenworth of New- York. 

199. Our practical rules may now be summed up and reca- 
pitulated, as follows, viz : 

1. The relative velocity of the circumference of the wheel 
appears to be, in all cases, about six and a half feet per second. 

2. Each horse power of engine, calculated according to the 
rules on page 121, will drive a paddle of the area of one-fifth 
part of a square foot with this velocity. 

3. The maximum absolute velocity of a paddle, to give the 
greatest velocity a boat has usually attained, is 26 feet per second ; 
but there are recent instances where as much as 29^ feet per se- 
cond has been reached ; and if the wave can be avoided, it would 
be unsafe, without a better theory of the motion of bodies in flu- 
ids than has yet been investigated, to name a limit which new 
improvements may not exceed. 

4. In a vessel of good model, these velocities may certainly be 
attained, when the relation between the area of the midship 
frame of the vessel, and that of the paddles of both wheels, is as 
three to one ; and they have been attained when the relation 
has been as small as 10 : 1. 

200. We cannot quit this subject without suggesting some 
views, which it is hoped may still further improve steam navi- 
gation. It has been seen that if the power of the engine be cal- 
culated according to the usual rule, each horse power ought to 
propel a surface of paddle equal to half a square foot j while in 
the two instances which we have cited the performances have 



NAVIGATION BY STEAM. 251 

been no move than .16 and .22 ft. In the one case, therefore, 
at least two thirds, and in the other more than one half the force 
estimated appears to be useless. It is obvious that this arises 
from the great velocity with which the piston of the engine is 
driven, in order to acquire the great velocities now usual in na- 
vigation. The whole tension of the steam acts as a pressure 
on the piston, only when that is at rest, and with every increase 
of velocity the pressure must be diminished. Experience de- 
rived from the action of engines employed in manufactures 
and pumping, would seem to show, that the maximum perform- 
ance of a condensing engine takes place, when the velocity of 
the piston is from 250 to 280 ft. per minute. It is now usual to 
drive those of steam-boats at rates between 400 and 600 ft. per 
minute. If the former numbers express one-third of the velocity 
which the piston would assume had it no work to perform, the 
defect in the performance of the engines of the North-America 
and President is almost exactly consistent with theory. On the 
other hand, it is absolutely necessary that the rotary velocity of 
the circumference of the paddle-wheel should not be less than 
26 feet per second, if the vessel is to move with the velocity 
which is now demanded. It would therefore appear, that a 
great saving of steam must accrue from such a disposition of the 
engine, as would allow its piston to move with no greater velo- 
city than 280 feet per minute, and should, notwithstanding, give 
one of 26 feet per second to the wheel. Two modes suggest 
themselves at once for accomplishing this object, namely, to in- 
crease the number of revolutions of the wheel by gearing, or to 
substitute for the crank the original contrivance of Watt, the 
Sun and Planet wheel. There is, however, an objection to the 
use of toothed wheels in steam-boats which is not unfounded, 
and if this be as positive as is usually thought, these methods 
are not likely to come into practical use. There remains, how- 
ever, another, which we have not seen suggested, namely, to 
make the arms of the lever beam of unequal lengths. In this 
way an engine of comparatively short stroke, and whose piston 
would in consequence move with a proportionally less velocity 
would give the necessary speed to the paddle-wheel, while the 



252 NAVIGATION BY STEAM, 

crank would still be applied at a favourable distance from the 
axis. 

The increase which has been given to the speed of the pad- 
dle-wheel is partly gained by an increase in the velocity of the 
piston, and partly by enlarging the diameter of the wheel itself. 
Adopting the method just suggested, the number of strokes of 
the piston might be increased, and the diameter of the wheel 
diminished. 

A similar advantage would be gained by the use of the Sun 
and Planet wheel. 

In steam vessels intended for the navigation of the ocean, the 
British nation has as yet been more successful than ourselves. 
They have, however, failed in giving them any thing like the 
velocity which we are in the habit of using. It would seem to 
be easy to give the American rate of motion to steam vessels, 
without impairing the good and sea-worthy qualities of the 
British steamers. In this event the mast and sails which they 
yet find of use, would be no more than a useless incumbrance, 
as our vessels outstrip even brisk gales of wind, and would, in 
consequence, find it always acting in opposition to them. More 
particularly is the bowsprit objectionable. The motion of a 
steam vessel, in her pitching is not, like that of an ordinary vessel) 
derived from the motion of the waves alone, but is, in addition, 
influenced by the action of the engine. It therefore will be of- 
ten struck by the waves in a high sea, and it is not wonderful 
that several accidents have already happened to this spar, in the 
few voyages that have been made between New-York and Great 
Britain. Not only is the bowsprit an incumbrance, and exposed 
to danger, but it is wholly unnecessary, even if it be admitted 
that steam vessels must be equipped with sails. The length of 
steam vessels is so great, that by lessening the after-sail, all the 
functions of the jib will be fulfilled by stay-sails spread between 
the cutwater and the foremast. 

If the speed of steam vessels on the ocean be increased to the 
American rate, sails may still be necessary in order to provide 
for accidents to the engine, or to spare the expenditure of fuel. 
It will not, however, be necessary to make any other provision 
for spreading them, than to step the lower masts, and reeve their 



NAVIGATION BY STEAM. 253 

standing rigging; the topmasts and top-gallant masts, with the 
yards, should bestowed away,. and only sent aloft when the ne- 
cessity for spreading sail arises. To one acquainted with the 
manner in which steam is used in our river steam-boats, and in 
which it may doubtless be applied on the ocean, the heavy masts, 
yards, and sails, with which the British steamers are incumber- 
ed, are not less offensive, than are the structures which we pile 
on the decks of our vessels, to the nautical eye. 

In the steam vessels for ocean navigation, the timbers ouo-ht 
to be carried up to the ievel of the upper deck, the whole plank- 
ed in, and strengthened by ceiling plank. Instead of the par- 
tial coverings of cabins and wheel-houses, the whole should be 
closed in by a spar deck extending from stem to stem, and if 
possible, flush. 

The great relative length which must be given to steam ves- 
sels, rendors them more liable to the usual tendency to the 
change of figure called hogging than other ships. They, in con- 
sequence, require to be proportionably stronger. This increase 
of strength is usually sought, by increasing the number and the 
scantling of the timbers. We conceive that this is wrong in 
principle, inasmuch as the weight of the vessel is the cause of the 
change of figure, and to increase it in adding to the strength of 
the material, may in the end render the evil which is to be con- 
quered greater. We should, in consequence, prefer to dimin- 
ish the scantling, and even lessen the number of timbers taking 
care that each shall constitute a frame ; and would propose to 
meet the tendency to change of figure by laying the ceiling 
plank diagonally, and by a system of lattice- work planking 
reaching from the keelson to the main-deck. In addition a series 
of iron stays, extending from the stem to the stern-post over 
the lower mast-heads, might be employed. 

The several frames ought to be united by bolts or rods of 
iron extending through three continguous timbers, and in such 
number, that every timber should be connected on each side 
with the second in distance from it. 

The engines employed should be of the character to which 
the name of portable is given ; that is to say, the whole of the 
parts which compose each of them should be united in a frame 



254 NAVIGATION BY STEAM. 

of iron. In this way the engine will act upon itself, and not 
upon the vessel. A horizontal ^engine is also to be preferred 
when it can be used, as a vessel is much less racked by its mo- 
tion than by one whose cylinder is vertical. 

The boilers should be of such a form as carry the least weight 
of water in proportion to their fire surface which is consistent 
with safety. For this reason, those with tubular flues are to be 
preferred. The only fuel which can be employed is coal, for 
the weight and bulk of wood would be an insuperable objection 
to its use on long voyages. Of the different kinds of coal, the bi- 
tuminous, under equal weights, gives the greatest quantity of 
heat, but generates so much smoke as to render the vessel un- 
comfortable for passengers. It is therefore probable that the 
mode of burning anthracite coal in boilers, with tubular flues, 
like those used in locomotive engines, and in which the igni- 
tion is promoted by a blowing engine, will be preferred. 

None of the vessels, which have yet been constructed for 
navigating the ocean, appear to us to be worthy of being cited as 
models to be copied. The English steamers are objectionable 
from the excessive and useless weight of their engines, and the 
great space they occupy ; and from the great size, and the weak- 
ness of their boilers. The steam frigate Fulton can hardly be 
considered as intended for ocean navigation. The Natchez, 
which runs as a packet between New-York and New Orleans, 
appears to unite a greater number of advantages than any other 
vessel, but has not sufficient tonnage to unable her to carry fuel 
for crossing the ocean. 

201. The steam engine, such as has been described in 
Chapter V., requires several modifications to suit it for the pur- 
pose of propelling boats. When placed in the middle of the 
vessel, that form represented in PI. VII., in which the great 
working-beam is suppressed, and two connecting-rods adapted 
to the piston by a cross-head, is often used. But when two en- 
gines are employed, the beam must be. retained. The cold- 
water cistern would load the vessel with an enormous weight, 
and hence the condenser is not immersed in water ; the hot- 
water cistern is, generally speaking, set upon the top of the air- 



NAVIGATION BY STEAM. 255 

pump ; and the delivering door is a conical valve surrounding 
the air-pump rod. Water for condensation is supplied by a 
standing-pipe, passing through the bottom of the boat and rising 
above the level of the external mass of fluid ; the injection-cock 
is below this level, and the water is forced into the condenser, 
by virtue of the difference of level. The waste hot water passes 
out by a similar pipe. These pipes are called standing pipes, 
and they are represented on PI. VII., at h h and / ; h h being 
the pipe adapted to the condenser, which it supplies through 
the injection-cock i, and I being the pipe through which the 
waste hot water is discharged from the cistern on the top of the 
air-pump H. A hand force-pump K, is employed to fill the boiler 
at first, and it is afterwards supplied by a force-pump I. The 
hand pump may also be employed to keep up the water in the 
boiler, when the engine is not in action. 

The condenser is increased to half, and the air-pump to one- 
third of the capacity of the cylinder. 

These standing pipes are exposed to danger, and the openings 
through which they pass are of such size that the slightest acci- 
dent, or even overloading, may be followed by the sinking of the 
vessel. It has, in consequence, been proposed to adapt valves to 
these openings, which might be shut in case of an accident hap- 
pening to the steam pipe, or of the vessel being loaded beyond 
her proper depth. Valves for this purpose have been invented 
in England by Kingston, and in this country by Mr. Haswell, 
the engineer of the U. S. Steam frigate Fulton. 

Another very important modification consists in the size of 
the valves and steam-pipes. It has already been seen, that in 
some cases, when steam acts expansively, the area of the nozzle 
should be increased; but in steam-boats the great velocity re- | 

quired for the wheels being usually gained, not by gearing, but 
by increasing the velocity of the piston, this can only be at- 
tained by affording a passage for an increased flow of steam. 
This method of increasing the speed has this advantage, that 
velocity is gained without increasing the weight of the engine, 
by merely adding to the fire surface of the boiler. 

In the steam-boats on the Hudson, not only has the velocity 
of the piston been increased by increasing the number of strokes, 



256 NAVIGATION BY STEAM. 

but by adding, at the same time, to the length of the cylinder. 
And, although it is obvious that in this way the pressure of steam 
of agiven tension in the boiler, upon the piston, must be lessen- 
ed, an equal area of paddle-wheel is driven. This we ascribe, 
in opposition to a high authority, to the fact that the crank of the 
engine acts in a more favourable point in the wheel. It would 
appear to us, that the true position of the extremity of the crank 
would be in the circle described by the centre of resistance of 
the paddle, and that it is only when applied to this circle, that all 
the force of the steam is applied to propel the vessel. Now, as it 
would be impossible to give the area of the crank so great a 
length as this, the nearer it approaches to it, the better. Hence, 
the method used in the American steam-boats has not only been 
successful in practice, but is founded upon true mechanical 
principles. 

The great length which is given to the cylinders of Ameri- 
can engines, and the supposed necessity of placing their bed 
plates so high that the axle of the wheels may lie below them, 
is attended with the disadvantage of impairing the stability of 
the vessel. Now, although a vessel ought not to be too stiff, 
because in that case the motion of rolling is violent, it seems 
probable that in our vessels there is not that degree of stability 
which is necessary for perfect safety. We have, therefore, to 
mention with approbation a very ingenious form of engine 
planned by Mr. Lighthall. In this, the cylinder lies in a hori- 
zontal position near the keelson of the vessel, and has the long 
stroke of the American boat engines. The motion of the piston 
is communicated to the wheels by straps working in guides, a 
lever beam, connecting-rod, and crank. The form is therefore 
similar to that of the engine on PI. III. provided it were laid 
upon its side. The manner in which Mr. Lighthall has pro- 
vided for the working of the pumps and valves of his engine is 
simple and sufficient. By means of this form of engine, all the 
advantages to be derived from length of stroke are secured, 
without any of the defects of the usual methods. 

The general form of the engine on PI. III. is now more used 
in steam-boats in the U. S. than that on PI. VII. The stroke of 
the piston, and the length of the connecting-rod and crank, being 



NAVIGATION BY STEAM. 25? 

greater in proportion to the height of the lever beam than in the 
first of these engines. The lever beam is not, as in PL III., a 
solid mass of cast iron, but is an open frame of that material 
surrounded by a strap of wrought-iron. 

202. The application of steam to the propulsion of vessels 
appears to have been among the very first ideas that suggested 
themselves to the inventors or improvers of the engine. Wor- 
cester, in the quotation that we have made from the " Century 
of Inventions," speaks of the capacity of his invention for row- 
ing. Savary proposed to make the water raised by his engine 
turn a water-wheel within a vessel, which should carry paddle- 
wheels acting on the outside ; and Watt, as we are well assur- 
ed by a personal auditor, stated in conversation, that, had he not 
been prevented by the pressure of other business, he would have 
attempted the invention of the steam-boat. Newcomen alone 
gave, as far as we can learn, no intimation of any such design ; 
and this we are rather to take as an evidence of his correct ap- 
preciation of the powers of his engine, than as arising from any 
want of ingenuity. In truth, before the time of Watt, no modi- 
fication under which steam was applied to useful purposes 
would have been able to propel vessels successfully. Even 
with all his improvements, the fuel is a great load, and its car- 
riage no small difficulty ; but, before he lessened its consumption 
so materially, it would have been hardly possible for a vessel to 
carry enough of combustible matter, except for very short 
voyages. 

Previous in date to all these persons, recent discoveries have 
brought to light an ancient record in which we have the de- 
scription of a vessel propelled by steam in a manner that ob- 
tained the suffrages of the witnesses. 

Blasco de Garay, an officer in the service of the Emperor 
Charles V., made, at Barcelona, in the year 1543, an experi- 
ment on a vessel, which he forced through the water by appar. 
atus, of which a large kettle, filled with boiling water, was a 
conspicuous part. If this be true, and we have no reason to 
doubt the authenticity of the records, De Garay was not only 
the first projector of the steam-boat, but among the first who 

33 



258 HISTORY OF 

conceived the idea of applying a steam engine to useful purposes* 
He was, however, too far in advance of the spirit of his age to 
be able to introduce his invention into practice, and even the 
recollection of his experiment had been lost, until the record 
was accidentally detected among the ancient archives of the 
province of Catalonia. This experiment was, therefore, with- 
out any direct practical result ; neither did it produce any effect 
in facilitating the researches of subsequent inquirers, and may 
therefore be considered rather as a matter of curious antiqua- 
rian research, than as deservedly filling any space in the history 
of the steam-boat. 

English authors have also raked up from oblivion a patent 
granted in the year 1736, to a person of the name of Jonathan 
Hulls. He, however, never made even an acting model of his 
invention, and the prime-mover itself was at the time in a state 
far too imperfect to have permitted its being successfully used 
in the manner proposed by Hulls. So far, then, from classing 
this among ingenious and profitable improvements, we should ra- 
ther be inclined to rank it among those which, from their ob- 
vious impracticability, merit the oblivion into which they in- 
stantly fall. 

The paddle-wheel, it has been stated, is the only apparatus 
that, when worked by steam, has been found completely success- 
ful in propelling vessels. The use of this for such a purpose, 
but set in motion by other prime-movers, is of remote antiquity, 
and was from time to time again brought forward, used for a 
season, and again abandoned. 

Among these attempts may be mentioned a boat constructed 
on the Thames by Prince Rupert, whose action was witnessed 
by Papin, by Savary, and probably by Worcester. So far as re- 
gards the antiquity of the method, Stuart quotes manuscripts 
from the library of the King of France, from which he states 
it was ascertained, that during one of the Punic wars, a Ro- 
man army was transported to Sicily upon vessels moved by 
wheels worked by oxen. The use of a water-wheel, in a man- 
ner the reverse of that in which it was employed to propel 
machinery, is almost too obvious to be entitled to the character of 
invention ; it was therefore only necessary that the necessity 



STEAM NAVIGATION. 259 

for their use should exist, and their introduction would have 
followed as a matter of course. 

It was, however, long questionable whether they could be 
used to advantage when attached to a steam engine, and in the 
earlier experiments, the blame appeared to fall upon them, ra- 
ther than upon the imperfections of the engine, or the unskil- 
ful and unartist-like manner in which they, and the rest of the 
apparatus, were adapted to the vessels. 

We have stated that Watt's engine was the first possessed of 
sufficient powers to be used to advantage in vessels. This is 
not merely an inference from what can be observed in the prac- 
tice of the present age, but was, in 1753, made a matter of ma- 
thematical proof by Bornouilli, in a memoir which gained a 
prize offered by the French Academy of Sciences. He, how- 
ever, expresses his opinion too broadly, applying his inference 
rather to the power of steam itself, than the mode in which it 
was then commonly applied. 

Still there were some who, not aware of the defects of th e 
prime-mover, continued to seek for the means of applying it to 
vessels. Among these may be named Genevois and the 
Comte d'Auxiron. The former, whose attempt dates as early 
as 1759, is chiefly remarkable for the peculiarity of his appar- 
atus, which resembled in principle the feet of aquatic birds, 
opening when moving through the water in one direction, and 
closing on its return. The latter made an experiment in 1774, 
but his boat moved so slowly and irregularly, that the parties at 
whose expense the trial was made, at once abandoned all hopes 
of success. 

In 1775 the elder Perrier, afterwards so celebrated as the in- 
troducer of the manufacture of steam engines into France, made 
a similar attempt, which was equally unsuccessful. But, not 
discouraged, and ascribing his failure to the use of paddle- 
wheels, he applied himself for some years afterwards to the 
search for other substitutes for oars. It does not appear, how- 
ever, that he made any valuable discovery. 

The Marquis de Jouffroy continued the pursuit of the same 
object. His first attempts were made in 1778, at Baume les 
Dames, and in 1781 he built upon the Saone a steam-vessel 



260 WATT. 

150 feet in length and 15 in breadth. In 1783 his experiment 
became the subject of a report made to the French Academy of 
Sciences, by Borda and Perrier. The report is said to have 
been favourable. 

We have seen that the double-acting engine of Watt was 
not made public before 1781, and that it was not until 1784 
that it received those improvements by which it was fitted 
to keep up a continuous and regular rotary motion. No pre- 
vious engine having the necessary properties, we feel warrant- 
ed in rejecting all attempts prior to the former date as prema- 
ture, in attempting to perform that to which the means in the 
possession of the projectors were inadequate. 

We are to look to our own country, not only for the first 
successful steam-boat, but for the very earliest researches into 
the subject, after the improvement of the engine by Watt had 
rendered success attainable. The very nature and circum- 
stances of the United States appeared to call for means of con- 
veyance different from those which are employed in other 
countries. Our whole coast is lined by bays and rivers, by the 
aid of which a safe parallel navigation, might, at small expense, 
be extended from one extremity of the Union to the other ; but 
which, land-locked, and protected from the winds, is at some 
seasons tedious to the ordinary methods. Still more recently, 
the Mississippi and its innumerable branches have become the 
seat of flourishing settlements, separated from the Atlantic 
coast by ridges of barren mountains, and almost inaccessible 
from the Gulf of Mexico by either sails or oars, in consequence 
of the rapidity of the stream. Our population, with the wants 
and curiosity of the highest civilization, is still scattered over 
so vast a region, as to demand rapid means of communication 
and great foreign importations. These wants could not have 
been satisfied, nor this active curiosity gratified, by any means 
yet discovered, except the steam-boat. The earlier projectors 
appear, however, rather to have reference to the prospective 
state of our country than to circumstances which existed at the 
moment of their attempts. Hence we shall find that they 
sought in foreign countries the encouragement, the wealth of 
their native land was inadequate to afford. 



RUMSEY — FITCH. 261 

Rumsey and Fitch were cotemporaneous in their researches. 
Both attempted to construct steam-boats as early as the year 
1783, and modes of both their contrivances were exhibited in 
1784 to General Washington. Rumsey's was the first in date 
of exhibition, but Fitch was first enabled to try his plan upon a 
scale of sufficient magnitude ; for, in 1785, he succeeded in 
moving a boat upon the Delaware, while Rumsey had not a 
boat in motion upon the Potomac before 1786. 

Fitch's apparatus was a system of paddles ; Rumsey at first 
used a pump, which drew in water at the bow and forced it 
out at the stern of his boat. The latter afterwards employed 
poles, set in motion by cranks on the axis of the fly-wheel of his 
engine, which were intended to be pressed against the bottom 
of the river. About the date of these experiments Fitch sent 
drawings of his apparatus to Watt and Bolton, for the purpose 
of obtaining an English patent ; and in 1789 Rumsey visited 
England upon the same errand. The former was not success- 
ful in obtaining patronage; but the latter, by the aid of some 
enterprising individuals, procured the means to build a vessel 
on the Thames, which, however, was not set in motion until 
after his death, in 1793. 

Fitch's boat was propelled through the water at the rate of four 
miles per hour. We may now reasonably doubt whether pad- 
dles would have answered the purpose upon a large scale, for 
more than one experiment on this principle has since been tried, 
and without success. The method of Rumsey is more obvious- 
ly defective, and we need not wonder that it was followed by 
no valuable results. 

Next in order of time to Fitch and Rumsey, we find Miller, 
of Dalswinton in Scotland. This ingenious gentleman had, as 
early as 1787, turned his attention to substitutes for the common 
oar, and had planned a triple vessel propelled by wheels. Find- 
ing that wheels could not be made to revolve with sufficient 
rapidity by men working upon a crank, the idea of applying a 
steam engine was suggested by one of his friends, and an engi- 
neer of the name of Symington employed by him to put the 
idea into practice. The vessel was double, being an experi- 
mental pleasure-boat on the lake in his grounds at Dalswinton. 



262 MILLER. 

The trial was so satisfactory, that Miller was induced to build 
a vessel sixty feet in length. This was also double, and it is 
asserted that it was moved by its engines along the Forth and 
Clyde canal at the rate of seven miles per hour. The boat, the 
wheels, and the engine, were, however, so badly proportioned to 
each other, that the paddles were continually breaking, and the 
vessel suffered so much by the strain of the machinery as to be 
in danger of sinking, and Miller found it unsafe to venture into 
any navigation of greater depth than the canal. The appara- 
tus was therefore removed and laid up, and here the experi- 
ments of Miller ceased. He himself appears evidently to have 
considered this experiment an absolute failure, and ascribed the 
blame to the engineer. We have to remark that the double 
boat used by Miller, was a form ill. suited to the purpose ; in 
the ferry boats of that structure, introduced by Fuiton into this 
country, the resistance growing out of the dead water included 
between the two hulls, has been found such, that they have 
been gradually abandoned, and single vessels substituted. 

John Stevens, of Hoboken, commenced his experiments on 
steam navigation in 1791. Possessed of a patrimonial fortune, 
and well versed in science, he was at the time wanting in the 
practical mechanical skill that was necessary to success ; he 
was hence compelled, at first, to employ men of far less talent 
than himself, but who had been educated as practical machinists. 
His first engineer turned out an incorrigible sot ; his second be- 
came consumptive, anddied before the experiment was completed. 
Stevens then resolved to depend upon his own resources, and 
built a workshop on his own estate, where he employed work- 
men under his own superintendence. In this shop he brought 
up his son, Robert L.Stevens, as a practical engineer, to whom 
many important improvements in steam navigation, and the 
most perfect boats that have hitherto been constructed, are due. 

During these experiments, Stevens invented the first tubular 
boiler ; and his first attempts were made with a rotary engine, for 
which, however, he speedily substituted one of Watt's. With 
various forms of vessels, and different modifications of propel- 
ling apparatus, he impelled boats at the rate of five or six miles 
per hour. They were, in truth, more perfect than any of his 



STEVENS — STANHOPE. "263 

predecessors', but did not satisfy his own high-raised hopes and 
sanguine expectations. These experiments were conducted at 
intervals up to the year 1807, and much diminished his fortune. 
"We must, however, pass from the detail of them, and the notice 
of the parties who became concerned with him, in order to 
speak of what was doing in Europe in the meantime. 

The Earl of Stanhope, in 1793, revived the project of Gene- 
vois, for an apparatus similar to the feet of a duck. It was 
placed, in 1 795, in a boat furnished with a powerful engine. 
He was, however, unable to obtain a velocity greater than three 
miles per hour. While engaged in these experiments, he re- 
ceived a letter from Fulton, who proposed the use of pad- 
dle-wheels ; and it is probable that his neglect to listen to this 
suggestion caused a delay in the introduction of the steam-boat 
of at least twelve years ; for we cannot doubt that the ingenui- 
ty of Fulton, backed by the capital and influence of Lord Stan- 
hope, would have been as successful then as it was on a subse- 
quent occasion. 

In the year 1797 Chancellor Livingston, of the state of New- 
York, built a steam-boat on the Hudson River. He was asso- 
ciated in this enterprize with a person of the name of Nisbett. a 
native of England. Brunei, since distinguished for the block ma- 
chinery, and as engineer of the London Tunnel, acted as their en- 
gineer. In the full confidence of success, Livingston applied 
to the legislature of the state of New- York for an exclusive 
privilege, which was granted, on condition that he should, with- 
in ayear, produce a vessel impelled by steam at the rate of three 
miles per hour. This they were unable to effect, and the pro- 
ject was dropped for the moment. 

In the year 1800 Livingston and Stevens united their efforts, 
and were aided by Mr. Nicholas Roosevelt. Their apparatus 
was a system of paddles resembling a horizontal chain pump, 
and set in motion by an engine of Watt's construction. We 
now know that such a plan, if inferior to the paddle-wheel, 
might answer the purpose ; it, however, failed in consequence 
of the weakness of the vessel, which, changing its figure, dis- 
located the parts of the engine. One of the workmen in their 
employ suggested the use of the paddle-wheel in preference, 



264 LIVINGSTON — EVANS. 

but, as Stevens candidly states, their'minds were not prepared to 
expect success from so simple a method. 

Their joint proceeding's were interrupted by the appointment 
of Chancellor Livingston to represent the American govern- 
ment in France, but neither he nor Stevens were yet discour- 
aged ; the latter continued to pursue his experiments at Ho- 
boken, while the former carried to Europe high-raised expec- 
tations of success. 

It has been stated that Symington was employed by Miller of 
Dalswinton as his engineer ; we have now to record an attempt 
made by him under the patronage of Lord Dundas of Kerse. 
Miller's views appear to have been directed to the navigation 
of estuaries and rivers, if not to that of the sea itself. Symington, 
on the present occasion, limited himself to the drawing of boats 
upon a canal. The experiment was made upon the Forth and 
Clyde canal, but the boats were drawn at the rate of no more 
than three and a half miles per hour, which did not answer the 
expectations of his patron, and the attempt was abandoned. 
During this attempt, Symington asserts that he was visited by 
Fulton, who stated to him the great value such an invention 
would have in America, and by his account, took full and am- 
ple notes. In the attempt he thus makes to claim for himself 
the merit of Fulton's subsequent success, he is defeated by the 
clear and conclusive evidence that Fulton exhibited in a court 
of law, of his having submitted a plan analogous to that after- 
wards carried into effect, to Lord Stanhope, in 1795, six years 
prior to the experiment of Symington. That Fulton, whose 
thoughts had continued to dwell upon steam navigation, and 
who saw with prophetic eye, the vast space for this development 
afforded by the Mississippi and its branches, should have visited 
all the places where steam-boats were to be seen, was natural ; 
but a comparison of the draught of Symington's boat, which 
is still extant, with the boats constructed by Fulton, furnishes 
conclusive evidence that the latter borrowed no valuable ideas 
from the former. 

In the same year, 1801, Evans made, at Philadelphia, an ex- 
periment of a most remarkable character. Being employed by 
the Corporation of that city to construct a dredging machine, 



FULTON. 265 

he built both the vessel and the engine at his works, a mile and 
a half from the water. The whole, weighing: 42,000 lbs., was 
mounted upon wheels, to which motion was given by the en- 
gine, and thus conveyed to the river. A wheel was then fixed to 
the stern of the vessel, and being again set in motion by the en- 
gine, she was conveyed to her destined position. Evans, how- 
ever, appears long to have abandoned the hopes of exciting his 
countrymen to enter into his projects of locomotion, and content 
with his steady business as a millwright, and the proof he had 
thus given of the soundness of his ancient projects, pursued the 
matter no farther. 

We have thus completed the review of those attempts at na- 
vigation by steam which were abortive, either from absolute de- 
ficiency, or from their not fulfilling the expectations of the par- 
ties interested. It is now our more gratifying task to record in- 
stances of complete success. Livingston, who, as we have stated, 
carried with him to France a sanguine belief that steam naviga- 
tion was practicable, met Fulton at Paris. They were imme- 
diately drawn to each other by similarity of views, and the latter 
undertook to make those investigations which the avocations of 
the other prevented him from doing. It occurred to Fulton that 
the first step towards success was to investigate fully the capa- 
bilities of different apparatus for propulsion. These preliminary 
experiments were made at Plombieres, and led to the conviction 
that of all methods hitherto proposed, the paddle-wheel possess- 
ed the greatest advantages. He next planned a mode of attach- 
ing wheels to the engine of Watt, ingenious in itself, but com- 
plicated, and which he afterwards simplified extremely. 

Up to this time the relation of the force of the engine to the 
velocity of the wheels and the resistance of the water to the 
motion of the vessel, had never been made a matter of preli- 
minary calculation. Aware, however, that upon a proper com- 
bination of these elements all positive hopes of success must 
depend, he had recourse to the recorded experiments of the So- 
ciety of Arts, and limiting his proposed speed to four miles per 
hour, planned his machinery and boat in conformity. The ex- 
perimental vessel was then constructed at Paris, and being 
launched upon the Seine, performed its task in exact conformity 

34 



266 FULTON. 

to his anticipations. It was then, as afterwards, remarkable, 
that by a sound view of theoretic principles, the single boats of 
Fulton always possessed the speed which he predicted at the 
moment of planning them. This was not the case when he 
attempted double vessels, in consequence of his leaving out of 
view that important resistance which was mentioned in speak- 
ing of Miller's vessel. 

This preliminary experiment was performed in 1S03. 
While Fulton was engaged in preparing for it, a person of the 
name of Des Blancs, who was possessed of a patent for apparatus 
for steam navigation, endeavoured to interrupt it as an infringe- 
ment on his rights. Fulton, however, communicated to him 
his preliminary experiments, in which he had found paddle- 
wheels superior to the chain of floats proposed by Des Blancs, 
and the opposition ceased. The trial on the Seine having 
proved successful, it was resolved to take immediate measures to 
have a boat of large size constructed in the United States ; but 
as at that time the work-shops in America were incapable of fur- 
nishing a steam engine, it became necessary to order one from 
Watt and Bolton. This was done, and Fulton proceeded to 
England to superintend its construction. In the meantime 
Livingston was sufficiently fortunate to obtain a renewal of the 
exclusive grant from the state of New- York. 

We here remark an anachronism in the work of Stuart. Sy- 
mington's own narrative, as given by that author, seems to place 
the interview with Fulton in 1801. Stuart, in a subsequent 
place, refers it to the date of this visit of Fulton's to Eng- 
land. We have previously stated it as happening at the former 
date upon Symington's authority, as this is alone consistent with 
the expression of astonishment that he records. For this could 
hardly have been uttered subsequent to the trial made upon 
the Seine. Each of the dates, however, causes a dilemma. If 
he saw Symington's boat in 1801, he returned to France with 
his previous impression in favour of paddle-wheels very much 
weakened ; if not until 1804, he had already performed more 
than Symington. 

In like manner the claim of Henry Bell, so pertinaciously 
maintained by British authors, falls to the ground. Bell claims 



FULTON — BELL. 267 

the merit of having furnished Fulton with the plan of his suc- 
cessful steam-boat on the ground of his having furnished 
plans and drawings, which he heard, two years afterwards 
from Fulton, were likely to answer this end. On receiving 
this letter, he states that " he was led to consider the folly of 
sending his opinions on these matters to other countries, and not 
putting them into practice in his own." Now, as Bell did not 
build his first boat until 1812, we cannot place the date of 
Fulton's second letter earlier than his return to America in 
1806, and that it was written from America Bell's expressions 
render evident. Fulton, therefore, could have derived no bene- 
fit from his advice, for his experiment in France was in 1803, 
and the engine of Watt and Bolton, which was first used on 
the Hudson, must have been ordered at least a year before the al- 
leged date of Bell's communications. Neither can we reconcile 
his claims with the statement made by his friends, that he was 
several years in bringing his plans to perfection, and his boat 
was, after all, very inferior to those constructed by Fulton seve- 
ral years earlier. The anxiety of the British public to transfer 
the honours of Fulton to Bell, is manifest from a report of a 
Committee of Parliament, where it is stated that Bell came to 
this country to construct boats for Fulton, while it is now ad- 
mitted that he never was on this side of the Atlantic. We ap- 
prehend, however, that the correspondence with Bell took place 
on a different occasion. When Fulton planned his ferry-boats 
for the East River (New- York), Jae proposed to make them 
double ; he therefore naturally desired to know something of 
Miller's vessel which he had never seen, and, by Bell's own 
statement, the request of Fulton for information was limited to 
that single object. Bell asserts that he furnished, in addition, 
views and plans of his own, but long before this time Fulton's 
boats were in successful operation, and many competitors had 
already appeared, not only in those places where an exclusive 
grant existed, but even within the waters of the state of New- 
York. 

The engine ordered from Watt and Bolton reached New- 
York towards the close of the year 1806, and the vessel built 



268 FULTON — STEVENS. 

to receive it was set in motion in the summer of 1807. The 
success that attended it is well known. 

In the mean time Livingston's former associate, the elder 
Stevens, had persevered in his attempts to construct steam-boats. 
In his enterprize he now received the aid of his son, and his 
prospects of success had become so flattering, that he refused to 
renew his partnership with Livingston, and resolved to trust to 
his own exertions. Fulton's boat, however, was first ready, and 
secured the grant of the exclusive privilege of the State of New- 
York. The Stevens's were but a few days later in moving a boat 
with the required velocity, and as their experiments were con- 
ducted separately, have an equal right to the honours of inven- 
tion with Fulton. Being shut out of the waters of the State of 
New- York by the monopoly of Livingston and Fulton, Stevens 
conceived the bold design of conveying his boat to the Delaware 
by sea, and this boat, which was so near reaping the honour of 
flrstsuccess, was the first to navigate the ocean by the power of 
steam. 

From that time until the death of Fulton, the steam-boats of 
the Atlantic coast were gradually improved until their speed 
amounted to eight or nine miles per hour, a velocity that Ful- 
ton conceived to be the greatest that could be given to a steam- 
boat. To this inference he was probably led by the observa- 
tion of the increased resistance growing out of the wave raised 
in their front. His three earlier boats, the Clermont, the Car of 
Neptune, and the Paragon, were flat bottomed, their bows form- 
ing acute curved wedges, "the several horizontal sections of 
which were similar. His last boats had keels, but they were in- 
troduced for no other purpose than to increase their strength. 
In the boats constructed by his successors after his death, a 
nearer approach was made to the usual figure of a ship, but the 
waves still formed an important obstacle. In the mean time the 
younger Stevens was steadily engaged in improving steam 
navigation, each successive boat constructed under his direction 
possessing better properties than the former. The view he took 
of the subject was different from that of Fulton ; believing that the 
great size of the wave was owing to defective form, he instituted 
experiments, both on a large and small scale, to determine the 



STEAM NAVIGATION. 269 

figure in which this obstacle is of least magnitude. On the set- 
ting aside of the exclusive grant of the State of New- York to Liv- 
ingston and Fulton, he prepared a boat for navigation of the 
Hudson, which performed its voyage at the rate of 13 and a half 
English miles per hour. 

Steam-boats were not introduced into Great Britain until 
1812, five years later than the successful voyage of Fulton. 
Bell, whose name has already been mentioned, built the first 
upon the river Clyde at Glasgow. In March, 1816, the first 
steam-boat crossed the British Channel from Brighton to Havre. 
Since that period their use has been much extended and their 
structure improved ; but, until lately, no European steam-boat 
had attained a speed of more than 9 miles per hour. 

In 1815 steam-boats, previously constructed by Fulton for 
the purpose, commenced to run as packets between New-York 
and Providence, Rhode Island, a part of which passage is per- 
formed in the open sea. One of these vessels had been intend- 
ed to make a voyage to Russia, but the greatness of the expense 
deterred the proprietors from undertaking it. This voyage was 
performed in 1817 by the Savannah, and in 1818 a steam-ship 
plied from New-York to New-Orleans as a packet, touching at 
Charleston and the Havana. 

In 1815 also, a steam-boat made a passage from Glasgow to 
London, under the direction of Mr. George Dodd ; but it was 
not until 1820 that steam-packets were established between 
Holyhead and Dublin. In 1825 a passage was made, by the 
steam-ship Enterprize, from London to Calcutta. All doubts, 
therefore, in respect to the practicability of navigating the ocean 
by steam might have been considered as settled. In point of 
economy, however, it can never compete with sails, and hence 
probably can only be used to advantage for conveying passen- 
gers, or for purposes of war. 

In the steam-boats of the Ohio and Mississippi, high-pressure 
engines are now in the most general use. The boilers are 
usually cylindrical, with internal flues ; and the favourite posi- 
tion of the cylinder is horizontal, resembling the engine on PI. 
IV. Many of them, however, have conical valves, which are 
necessarily placed in vertical boxes ; this has demanded a novel 



270 STEAM CARRIAGES. 

arrangement of the steam and eduction pipes, and of the appar- 
atus for working the valves. 

In France, Steam navigation has been of even more recent in- 
troduction than in England. Five years, as we have seen, 
elapsed from the time of Fulton's successful voyage until Bell 
navigated the Clyde, four more passed before a boat, built in 
England, crossed the Channel, and proceeded up the Seine to 
Paris. 

As steam navigation took its rise on the Hudson, so the 
steam-boats navigating that river have uniformly been before 
all others in point of speed. The passage to Albany does not 
at present (1839) average more than 10 hours, which is at the 
rate of nearly fifteen miles per hour. It is stated by Mr. Red- 
field, that the maximum velocities are 16 miles per hour, that 15 
miles per hour is no unusual rate, and 14 may be considered as 
an ordinary performance on the Hudson river. The first boats 
which approached to this degree of speed were constructed under 
the direction of R. L.Stevens. Others, however, speedily follow- 
ed ; and the attainment of such velocities, which European wri- 
ters even at the present moment declare to be impossible, is due 
to the competition which has existed upon the Hudson. 

The speed of which we speak, has been obtained by increas- 
ing the length of the stroke of the piston, the area of the steam- 
pipes and valves, the diameters of the wheels, and by changes 
in the form of the vessels, to which false prows have been adapt- 
ed as experiments, until the figure of least resistance seems in 
some cases to have been reached. In some of the newer vessels 
the model has reached such a degree of perfection that no wave 
is raised at the bow, and no depression caused at the stern of 
the vessel. Above all, the expansive action of the steam has 
been employed, by means of which a given engine can be driven 
with greater velocity, and at a diminished cost. 

Others have approached this same speed so nearly, that the 
difference of passage has not been many minutes in the distance 
of nearly 150 miles. In a passage made by the author, on the 
Hudson, in 1829, the wheels of the New-Philadelphia averaged 
25£ revolutions per minute ; and the piston moved with a velo- 
city of 405 feet per minute, being 2L feet more than has been 



STEAM CARRIAGES. 271 

stated on a former page as the velocity of those of the North- 
America. Since that time the velocities of the pistons of steam- 
boats have been still further increased, and have in some cases 
amounted to as much as 600 ft. per minute. 

204. The first attempt to navigate the ocean by steam was 
made, as we have seen, by John Stevens of Hoboken, in the 
year 1809, when he sent a vessel, originally constructed for a 
ferry-boat, from New- York to Philadelphia, around the capes 
of the Delaware. 

In the summer of 1815, the first steam vessel built on the 
Clyde by Bell made a passage from Glasgow to Liverpool, and 
during the autumn of the same year several other vessels, also 
built on the Clyde, were sent to different parts of England. 
During the equinoctial storm of 1816 one of these crossed from 
Brighton to Havre, in a gale which the cutter packets employed 
at that time on the station were unable to weather. 

The practicability and safety of navigating the stormy seas 
which surround the British Islands being thus demonstrated, 
the British Government was not long in undertaking to esta- 
blish lines of packets for the conveyance of its mails. The 
first line was established between Holyhead and Dublin, and 
has been in successful operation for twenty years. It is said 
that they have rarely failed in sailing at the appointed time, 
and have met with few or no accidents. 

Before the death of Fulton, he had planned a vessel which 
was intended to be used on the Baltic. This vessel was in a 
state of forwardness at time of his death. Circumstances pre- 
vented his successors from sending this vessel on her destin- 
ed voyage, but she was placed as a packet between New- York 
and Newport, R. I. in which passage the open sea is navigated 
for a short distance. The very voyage contemplated by Fulton 
was effected in 1818 by a vessel built in New- York, called the 
Savannah. The Savannah made her passage from New-York 
to Liverpool, partly by steam and partly by the aid of sails, in 
26 days. From Liverpool this vessel proceeded around Scotland 
to the Baltic, and up that sea to St. Petersburgh. In returning 
thence she touched at Arendahl in Norway, and. without ma- 



272 STEAM CARRIAGES. 

king any other intermediate port, reached New- York in 25 

days. 

During the year 1819, a vessel rigged as a ship, but furnish- 
ed also with a steam engine, was built at New- York, for the 
purpose of plying as a packet between that port and Charleston, 
Cuba, and New-Orleans. So far as safety and speed were con- 
cerned, the experiment was successful ; but after several passa- 
ges it was found that the number of passengers was not suffi- 
cient to defray the expense, and the scheme was abandoned. 
The vessel was of such excellent model and construction, that 
she was purchased by the Brazilian government for a cruizer, 
and was as late as 1838 still in existence in that service. Be- 
fore this, however, the engine was taken out, and no other mode 
of propulsion employed except her sails. This vessel was con- 
structed under the direction of Mr. Jasper Lynch, who had ac- 
quired his knowledge of the use of the steam-engine from Ful- 
ton. The experiment, although a failure in point of profit, was 
worthy of the most complete success. The vessel had admir- 
able properties both as a sea-boat and a sailer, and the speed 
was not less than that which the best English steamers have 
reached up to the present time. Nothing was wanting except 
a sufficient tonnage to have enabled this vessel to cross the At- 
lantic in a time as short as that employed by the Great Western 
and Liverpool. 

The regularity and safety with which the passages between 
Holy-Head and Dublin were performed, established the fact of 
the superior safety of steamers in stormy and dangerous seas. 
Lines of packets were, in consequence, speedily established be- 
tween different points of the British Islands, and from Great 
Britain to the continent. Communications by steam have 
long existed to Hamburgh, Rotterdam, Antwerp, Calais, and 
Havre ; and there are numerous steam packets plying between 
different ports of England and Ireland. The most important 
line is that between London and Leith, in which the largest 
steam vessels built before those intended for the navy or for 
crossing the Atlantic, were employed. 

The British Government has gradually extended its lines of 
communication to Lisbon, Gibraltar, Malta, and Corfu. It has 



STEAM CARRIAGES. 273 

had it also in contemplation to extend them to Syria, in order 
to reach the Euphrates by land, and thence to establish steam- 
packets to Bombay. A company has also been formed for build- 
ing steamers to proceed to India by the way of the Cape of 
Good Hope. 

The first voyage to India by steam was performed in 1825, 
by the Enterprize. This vessel took her departure from Fal- 
mouth, and was 47 days between the Cape of Good Hope and 
Calcutta. As in the passage of the Savannah, the voyage was 
performed by the alternate aid of wind and steam. 

In spite of these experiments, of greater or less promise, it 
was seriously maintained by no mean authority, as late as Au- 
gust 1838, that the passage of the ocean, as a regular business 
by steam vessels, was impracticable. The most that could be 
hoped, as was alleged, would be to pass from the most western 
ports of Europe to the Azores or Newfoundland, and then 
take in a fresh supply of fuel. 

In the face of these discouraging predictions, the direct pas- 
sage from a port in Great Britain to New- York was made al- 
most simultaneously by two steamers before the end of the 
year in which the argument was held. Of these vessels, one 
(the Great Western) had been built for the express purpose, and 
had a tonnage adequate to the great probable consumption of 
fuel ; the other (the Sirius) was of the very class which had 
furnished the basis of the opinion ; and yet the fuel which could 
be carried was not entirely exhausted. It is therefore establish- 
ed beyond all possibility of doubt, that steam vessels, if they 
have the capacity of 12 to 1400 tons, may perform the direct 
passage from England to New -York by steam alone. It would 
also appear that no difficulty need exist in combining the sea- 
worthy qualities of the English steamers with the rapid motion 
of the American steam-boats ; and this may be effected, along 
with a considerable saving in fuel, and a great reduction of 
the weight of engine, boiler, and water. With such reduc- 
tions the carriage of many tons of cargo, as well as of passen- 
gers, will become possible, and the profits of the speculation will 
be placed upon a secure basis. 

The form of the engines and boilers of the British steamers 

35 



274 . STEAM CARRIAGES. 

which have crossed the Atlantic, does not materially vary 
from that given in PI. VIII. The required increase of power 
has been given by enlarging the diameter of the cylinders be- 
yond the proportion which is there exhibited ; and the extent of 
iron frame-work in which the engine is supported and kept to- 
gether, has been enlarged. The proportions of the cylinder, and 
the manner in which two working beams are suspended from 
the piston rods in each engine, have been adopted with a view 
to ensure the stability of the vessel by placing the weight as low 
as possible. So long as the masts and sails of steamers approach 
in weight and extent to those of ordinary vessels, this is no un- 
wise precaution ; but as we firmly believe that sails might be 
dispensed with, this reason will no longer exist. The weight 
of these beams in particular is much greater than is admitted in 
American engines of equal power, where, instead of solid masses 
of cast-iron, a light frame-work of that material, surrounded by 
a strap of wrought iron, has been substituted, with a positive gain 
of strength. 

The boilers of the English vessels are of a form which is 
very weak, the flues are of great size, and the quantity of water 
is much greater in relation to the fire surface than is admitted 
in the American practice. While, therefore, we have to admire 
the sagacious views with which a sufficient capital to build 
such noble vessels has been contributed, and contrast it with 
the limited scale on which the navigation of the ocean has 
been attempted in this country, we believe that great improve- 
ments remain to be made, by the introduction of the methods 
which we have cited as having contributed to give the great 
speed, which has been attained in the river boats of the United 
States. This is nearly one half more than has yet been reach- 
ed in Europe, and with it there can be no doubt that the pas- 
sage may be accomplished in 12 days. 

205. The subject of the explosion of steam boilers has recently 
attracted a great share of public attention. A vast number of 
facts, and a great variety of written opinions, have been collect- 
ed by the Secretary of the Treasury, and published by order of 
Congress. Among these papers we may quote, for the infor- 



STEAM CARRIAGES. 275 

mation of our readers, one by Mr. Redfield of New- York. This 
gentleman adopts a different view of the subject from that given 
by us in Chap. II. Still the results at which he arrives are in 
strict conformity with those derived from the other theory, and 
are therefore to be implicitly relied on. 

" If high-pressure engines must continue to be used, (of 
which I see not the utility or necessity,) the working pressure 
should never exceed fifty pounds to the square inch ; and this 
may be easily effected by increasing the size and stroke of 
the working cylinders and piston. The forms of the boilers 
should be cylindrical, and their diameters from 36 to 42 inches, 
supported by their centres as well as at their terminations. Flues, 
if of a size affording but one or two in each boiler, are always 
dangerous ; they displace too much water, and also obstruct the 
proper cleaning. Flues, however, are not to be dispensed with, 
but their number ought to be increased and their size diminish- 
ed. An upper tier of four flues, and a lower tier of two, (the 
latter somewhat larger than the former,) are not too many for 
boilers of 42 inches in diameter ; or 44 to 48 inches, if low pres- 
sure. These smaller fines, if properly arranged, will greatly fa- 
cilitate the cleaning, and displace but little water; but their 
length should not usually exceed ten or twelve feet, as they ab- 
stract heat very rapidly. They will be better if made perfectly 
smooth on their inner surface, from a single long sheet of iron, 
lighter than the shell ; and are not often liable to leaks or acci- 
dents. The outer shell should never be less in thickness than 
a full quarter of an inch ; and a thickness much exceeding this, 
it is well known, cannot be used with advantage. 

"In condensing engines which work expansively, called low- 
pressure, when working with ordinary speed, the pressure of 
the steam should usually range between one and one and a 
half atmospheres above the boiling point. But on emergencies 
the pressure may be increased to two atmospheres. The boilers 
should have a range of strength falling but little short of 
those used for high pressure. They may be constructed in the 
common wagon top form, provided that they are properly braced 
in their flat sides and arches, and have as many as four or six flue- 
arches for a boiler of eight or ten feet in width. The returning 



276 STEAM CARRIAGES. 

flues should be cylindrical, and of smaller diameter. The 
water-sides, water-bottoms, bridge-walls, and other flat surfaces, 
should, however, be brace-bolted at intervals of six inches ; and 
the arches, shell, and all other portions, secured in a propor- 
tionate manner. If a steam- chimney is used, even of the cir- 
cular form, it should be brace-bolted at smaller intervals than 
any part of the flat surfaces which are covered by water." 

206. Steam is also employed to move carriages upon the 
land. For this purpose, the wheels of the carriage are set in 
motion by the engine, in the same manner that the paddle- 
wheels of a steam-boat are caused to turn ; the friction which 
they experience upon their track causes them to move forward, 
unless they meet a resistance to their progressive motion equal 
to this friction. The experiments of Coulomb and Yince show 
that, under the circumstances in which wheels act, the friction 
of their circumference will depend upon the weight with which 
they are loaded, and the nature of the rubbing surface, but not 
in the least upon the velocity. The tire of wheels is made of 
iron, and steam-carriages usually run upon tracks, also of iron, 
forming what is styled a rail-road. Rail-roads are parallel bars 
of iron, laid either level, or with a gentle and uniform slope ; and 
steam has, as yet, only been usefully applied to locomotion up- 
on roads of this character. The reasons why they should be 
superior in this respect to a common road are obvious. The 
resistance is not only regular and uniform, but equal upon 
every wheel ; while on a common road there is a constant vari- 
ation in slope, and in the nature of the surface ; and besides, 
obstacles are frequently met that affect but one of the wheels, 
and thus tend to turn the carriage to one side. There is thus 
a want of continuity in the motion of the carriage, a lateral sliding 
friction of the wheels upon the road, and one arising from 
penetration into the materials of which the road is made. In 
addition, the friction of the wheel upon the shoulder of the axle 
and on the linch pin, is of great amount on a common road. In 
spite of these difficulties, some tolerably successful experiments 
liave been performed with steam-carriages upon common roads. 

The^ase, however, that is most usual as well as most advan- 



STEAM CARRIAGES. 277 

tageous, is motion upon rail-roads. Here the friction is that of 
iron against iron. We cannot anticipate that the wheels will 
be prevented from sliding upon a rail road by the maximum 
friction that takes place between two pieces of iron in experi- 
ments 5 dust, moisture, and other circumstances interfere to 
lessen the adhesion. It cannot, therefore, be safely taken at 
more than ith part of the weight. If there be a force applied, 
sufficient to cause the wheels of a carriage to turn around, it 
will continue to go forward until the resistance becomes equal to 
£th of the weight of the carriage. The carriage is, therefore, 
under the same circumstances as if it were drawn forward by 
a cord capable of bearing a strain of fth part of its weight. 

The resistances to the progressive motion are the friction 
upon the axis of the wheels, and the disturbances growing out 
of lateral shocks. The friction of steel axles upon brass boxes, 
well coated with oil, is -^th part of the weight; and the 
force applied to overcome it has its intensity increased in the 
ratio of the radius of the crank to the radius of the axle. As 
the radius of the crank of an engine of a given power cannot be 
increased without diminishing the area of the piston or its own 
velocity, there is no gain of force by simply varying the propor- 
tions of its engine. On the other hand, as with an equal num- 
ber of revolutions, points will move faster on the circumference 
of a larger wheel than they will on a smaller one, and the pro- 
gressive motion will depend on the velocity of the circumference, 
there is a const ant and regular gain in velocity, by increasing 
the diameter of the wheels. This, however, has its limit in 
practice, for, by increasing the diameter of the wheels, the cen- 
tre of gravity is raised, and the machine becomes unstable. 

According to the best experiments and observations, the fric- 
tion of carriages upon rail-roads has been in some cases dimin- 
ished to ^-J-y th ; and may be safely taken as not more than 
2-J— th. A locomotive carriage, therefore, all of whose wheels are 
driven by the engine, may move forward if it drag behind it 
any weight less than thirty-two times its own. 

It might, at first sight, appear that, as the friction which 
causes the carriage to go forward increases with its weight, 
heavy carriages and engines were the best for locomotion ; but 



278 stbam carriages. 

the resistances increase also with the weight, and thus all 
weights, not absolutely essential to the structure of the engine, 
are disadvantageous. Hence, for locomotion, no other en- 
gine but that of high pressure can be admitted : for condensing 
engines of equal power are not only heavier in themselves, but 
require a quantity of cold water for condensation, that would, 
of itself, furnish a load for the engine. So also the boiler and 
the load of water, should be. the smallest that is consistent with 
the generation of the necessary quantity of steam. 

The workmanship of the carriages used on rail-ways has 
been regularly improved for several years past, and probably 
has not attained perfection. The want of perfection in the 
workmanship, and perhaps the absolute impossibility which 
exists of making all the wheels of equal diameter, has led to 
the practice, in rapid motions, of giving no more than one pair 
of wheels a motion from the engine. This pair bears little more 
than half the weight, and hence the propulsive power is appar- 
ently less than if all the wheels were driven. This loss, how- 
ever, is not real ; for the sliding of wheels, not absolutely equal 
in diameter, will consume more power than is apparently lost. 

On the other hand, in slow motions, and in the ascent of in- 
clined planes, heavy engines, of which all the wheels are driven 
by the engine, are employed. 

A vast improvement has taken place in the performance of 
locomotive engines since the publication of our first edition. 
At that time we did not venture to state the actual draught of 
a locomotive at more than seven times its own weight. We 
are now enabled to rate it as high as thirty-two times as much 
as rests on the driving wheels. With an engine of the weight 
of 8 tons, the load has been as great as 175 tons, or more than 
40 times the weight which rests on the active wheels ; and the 
velocity with this load is 12.^ miles per hour. In doubling the 
load, the velocity is diminished to |th, while in a given dis- 
tance the expenditure of fuel is diminished one half. 

An engine constructed by H. R. Dunham &. Co. of New-York 
for theHarlaem Rail Road weighed 20,400 lbs. or about 9 tons ; 
the boiler being full of water, and the engine in working order. 
Of this weight 10,680 lbs. bore on the driving wheels. The 



STEAM CARRIAGES. 279 

load drawn was 105 tons upon 35 cars, whose weight is not 
given. The road was not level, and the slopes were from 25 to 
30 feet per mile. 

A locomotive engine is propelled in all cases by steam of 
high pressure. This mode of employing steam is rendered 
necessary by the great quantity of water required in condensa- 
tion, which would of itself furnish a large part of the load 
which can be drawn. The cylinder of the engine has been 
usually placed horizontally, or but little inclined. Some of 
those on the Baltimore and Ohio Rail Road have been placed 
vertically. Two cylinders are generally used, acting upon 
cranks on the axle of the same pair of wheels, at right angles 
to each other. In this way one piston is at its maximum ac- 
tion while the crank of the other is passing the centres, and 
greater regularity of motion is ensured. When the other 
wheels are to be set in motion, they are united with the first 
pair by means of connecting rods. We have already stated in 
what cases all the wheels are to be driven, and when no more 
than one pair. 

In the former case no more than four wheels are used. In 
the latter case, after trying curricle engines, those with six 
wheels have been found most serviceable. The English en- 
gineers place the driving wheels, which are of greater diameter 
than the remaining four, between the other two pairs. In the 
American engines the driving wheels are at one end of the 
carriage, and the four others are united in the same frame on 
which the opposite end bears. Engines of this form, of great 
perfection of workmanship, have been constructed by various 
artists, of whom the most celebrated are Baldwin and Norris. 
We have obtained, as an illustration of this part of the subject, 
a draught of a locomotive by Dunham of New- York. This is 
represented on PI. IX., and is a specimen of the form now con- 
sidered as most advantageous. An engine with six wheels was 
first planned in the year 1826 for the Mohawk and Hudson 
Rail Road, by Mr. J. B. Jervis. 

In order to compare the action of steam upon rail-roads, 
with its performance in propelling boats, we have the following 
principles : — 



280 STEAM CARRIAGES. 

Friction opposes a resistance which has a constant measure 
at all velocities ; but the measure of the power required to over- 
come it, will depend both on the resistance and the velocity. 
Hence the powers of engines, by which different velocities are 
obtained in the same carriage, are proportioned to the velocities. 
But as the time for passing over a given space is inversely as 
the velocity with which the distance is performed, a given dis- 
tance should be performed, with a constant load, at any velocity 
whatever, with a constant expenditure of fuel. 

If the same locomotive engine have its velocity increased by 
lessening the loads it drags or diminishing the friction, by both of 
which methods a limited change in velocity maybe attained, the 
expenditure of steam has been found to increase in a higher 
ratio than the velocities. This arises from the fact, to which 
we have more than once referred, that the action of steam of 
a given tension on the piston of an engine is diminished, when 
the velocity is increased. Were it not so, the expenditure of 
steam should be in this case proportioned to the velocities. 

It is therefore obvious, that when speed is the sole object in 
view, locomotion on land soon becomes more advantageous 
than steam navigation, for the power in the latter case increases, 
according to the received theory, as the cubes of the velocities ; 
and the expenditures of fuel as the square. Even if the view 
which we have presented as more consistent with the facts, be 
true, the power must be increased as the squares, and the ex- 
penditure of fuel with the first power of the velocities. On 
the other hand, friction on rail-roads has not yet been so much 
diminished as to enable them to compete either with steam or 
canal navigation, in the conveyance of heavy loads at small 
velocities. The friends of rail-roads have anticipated that 
they will soon be enabled to lessen the friction so much as to 
place them, in all respects, on a par with either of the other 
species of transportation. It would, however, appear, both from 
theory and experience, that unless when a saving of time is the 
principal object, the application of steam to navigation is more 
advantageous than to the rail-road. 

207. Evans, as has been already mentioned, was the first 



STEAM CARRIAGES. 28i 

who entertained rational hopes of being able to move carriages 
by steanij for we must reject the views of Robison and Watt as 
wholly impracticable ; and indeed the impossibility of using 
the condensing engine was ascertained and admitted by Watt. 
Evans not only was the first to entertain correct views, but was 
also the first to submit them to practice, in the removal of his 
dredging machine, which has been before referred to in the pre- 
sent chapter. 

In 1802 Trevithick and Vivian took out a patent for the 
application of their engine to propel carriages upon rail-roads, 
In 1804 they published a description of a carriage intended for 
common roads, but it was not until 1806 that an actual ex- 
periment was made. This was performed upon the Merthr 
Tydvil Rail-Road, in Wales. The performance of the appar- 
atus was, however, far less than might have been anticipated 
from its power, and this was ascribed to a want of sufficient 
adhesion of the wheels to the rail. We recollect having heard 
this failure ascribed to the circumstance that but one of the 
wheels was set in motion by the engine ; but all the authorities 
that we have consulted seem to agree, that all the four wheels 
were made to revolve. 

The failure, which, had the first statement been true, is at 
once to be accounted for, becomes difficult to explain if these 
authorities state the real circumstances. 

A difficulty, however, in the use did occur, and being ascrib- 
ed to the cause that has been mentioned, a person of the name 
of Blenkinsop undertook to obviate it. For this purpose he 
laid a rack, or rail cut into teeth, between the other two rails, 
along the whole extent of road : into this a pinion, set in mo- 
tion by the engine, caught. This method was found effectual 
at slow velocities, and was used from the year 1801, in which 
it was invented, nearly up to the present time, at Middleton 
Colliery, near Leeds in England;, It will not admit of great 
velocities, but is applicable to the rising of ascents far more 
steep than can be overcome by the mere adhesion of the wheels 
to the road. 

In 1812, Messrs. W. & E. Chapman obtained a patent in 
England for a locomotive engine, the power of which was ap- 

36 



282 STEAM CARRIAGES. 

plied by means of a chain fixed at the two ends, and passing 
over an axle upon the carriage that was caused to revolve by 
the engine. 

In 1S13 Mr. Brunton, of Batterly Iron Works, proposed a 
plan for locomotion by steam, in which he employed a system 
of levers, resembling, in their action, the bones of the human 
leg. 

In 1815, Dodd and Stephenson, of Killingworth, in England, 
returned to the original principle of adhesion, and were com- 
pletely successful, showing that on rail-roads, absolutely or 
nearly level, the friction was sufficient to produce progressive 
motion in all cases except when the rails were covered with 
snow. Their engine had six wheels, two of which were 
moved by the engine, and the others connected with them by 
an endless chain passing over drums. 

Locomotive engines have received, since that time, continual 
improvements. Two cylinders have been used, each acting 
upon a pair of wheels. The next step was to use two cylin- 
ders acting at right angles to each other upon the same pair of 
wheels, and to move the others by connecting rods. 

In these several improvements, the weight of the engine and 
its parts were gradually increased to an excessive amount. 
The centre of gravity was also raised so high as to render the 
carriages unstable. In consequence of this, a search has more 
recently taken place for engines and carriages of small weight. 
This has been successful in a remarkable degree, in locomotive 
engines exhibited upon the Manchester and Liverpool Kail- 
Roads. The details of these experiments are to be found in 
the Mechanics' Magazine for November and December, 1 829, 
and in the Quarterly Review for March, 1830, to which we re- 
fer our readers. 

The Baltimore and Ohio Rail-Road was projected, and some 
parts of it finished, as early as the Manchester and Liverpool. 
It also became the seat of a number of experiments, and these 
have been continued upon it, and on other more recent rail- 
roads, until such a degree of perfection has been reached in the 
structure of locomotive engines in the United States, that they 
have been made an article of export. 



CONCLUSION. 283 

20S. In concluding this work, a few reflections on the impor- 
tance of the subject may not be irrelevant. The steam engine 
has been described in its most usual and most perfect forms ; 
in the historical sketch, it has been traced from the earliest no- 
tices of the knowledge of the mechanical power of steam, down 
to the present time, when it occupies so important a space 
among the productions of human skill. Feeble and imper- 
fect in its first beginnings, and limited, for nearly a century 
after its introduction, to a single, and by no means important 
object, it became in the hands of Watt an instrument of 
universal application. It is now equally subservient to those 
purposes which require the greatest delicacy of manipulation, 
and those which demand the most intense exertions of power. 
Its introduction and gradual improvement have required in- 
ventive talents of the highest order, and the exertions of genius 
the most sublime ; in its uses we see developed and realized, 
not only the brilliant conceptions of poetry, but the wildest fa- 
bles of romance ; it has already changed the state of the world, 
and altered the relations of civilized society ; and in its farther 
progress it seems to promise to perform even more inportant 
services, and to fulfil yet higher destinies. 



APPENDIX. 



ANALYSIS OF A NEW THEORY 



THE STEAM ENGINE 



THE CH. G. DE PAMBOUR. 



The following analysis of a new theory of the Steam Engine, made 
by its author, from the full exposition which he has laid before the 
French Institute, will be found to possess much interest. Before it 
was received, the second edition had been prepared for the press ; and, 
even had it been judged expedient, it would have been too late to 
adopt it as the basis of practical rules. It may, however, be stated, 
that however fully we concur in the views of the Chev. de Pambour, 
it would have been premature to adopt it until it had received a more 
general sanction ; and that its assumption might have for a time un- 
fitted our own work for the use of practical men. It is therefore an- 
nexed as an Appendix, for the purpose of giving it circulation, and 
preparing the public mind for its reception in the place of that of 
Robinson, which has hitherto formed the basis of all treatises on the 
Steam Engine, and from which, although aware of its defects, we 
have not ventured to deviate. 



288 



PART I, 

PROOFS OF THE INEXACTITUDE OF THE ORDINARY METHODS^ AND 
EXPOSITION OF THE ONE PROPOSED. 

§ 1. Mode of calcidation hitherto in use. — All the problems in 
the application of steam-engines merge into these three — 

The velocity of the motion being given, to find the load the en- 
gine will move at that velocity. 

The load being given, to find the velocity at which the engine will 
move that load ; 

And, the load and the velocity being given, to find the vaporiza- 
tion necessary, and consequently the area of heating surface re- 
quisite for the boiler, in order that the given load be set in mo- 
tion at the given velocity. 

The problem, which consists in determining the useful effect to be 
expected from an engine of which the number of strokes of the pis- 
ton per minute is counted, that is, whose velocity is known, evident- 
ly amounts to determining the effective load corresponding to that ve- 
locity ; for that load being once known, by multiplying it by the ve- 
locity we have the useful effect required. 

According to the mode of calculation hitherto admitted, when it is 
Wanted to know the useful effect an engine will produce at a given 
velocity, or, in other words, the effective load that it will set in mo- 
tion at that velocity, the area of the cylinder is multiplied by the ve- 
locity of the piston, and that product by the pressure of steam in the 
boiler ; this gives, in the first place, what is called the theoretical efc 
feet of the engine. Then, as experience has shown that steam-en- 
gines can never completely produce this theoretical effect, it is re- 
duced in a certain proportion, indicated by a constant number, which 
is the result of a comparison between the theoretical and practical ef- 
fects of some engines previously put to trial ; and thus is obtained 
the number which is regarded as the practical effect of the engine, or 
the work it really ought to execute. 

A mode perfectly similar is followed, for determining the vapori- 
zation which an engine ought to produce in order to produce a de- 
sired effect ; that is to say, for resolving the third of the problems 
which we have presented above. As to the second of these problems, 



289 

that which consists in determining the velocity the engine will as- 
sume under a given load, no solution of it has been proposed in this 
way, and we shall expose, farther on, some fruitless essays that have 
been made to resolve it in another way. 

As in the above-mentioned calculation no account is taken of fric- 
tion, nor of some other circumstances which appear likely to dimin- 
ish the power of the engine, the difference observed between the 
theoretical and the practical result excites no surprise, and is readi- 
ly attributed to the circumstances neglected in the calculation. 

§ 2. First objection against this method of calculation. — This 
mode of calculation is liable to many objections, but for the sake of 
brevity we limit ourselves to the following :— 

The coefficient adopted to represent the ratio of the practical effects 
to the theoretical, varies from ■£■ to ■§, according to the various systems 
of steam-engines ; that is to say, that from ■§■ to -*- of the power exerted 
by the machine is considered to be absorbed by friction and divers 
losses. Not that this friction and these losses have been measured 
and found to be so much, but merely because the calculation that had 
been made, and which might have been inexact in principle, wanted 
so much of coinciding with experience. 

Now it is easy to demonstrate that the friction and losses which 
take place in a steam-engine can. never amount to f, nor to -*- of the 
total force it developes. It will suffice to cast an eye on the explana- 
tion attempted, on this point, by Tredgold, who follows this method 
in his Treatise on Steam-Engines.* He says (art. 367,) that, for 
high pressure engines, a deduction of -^ must be made from the to- 
tal pressure of the steam, which amounts to a deduction of -^ on the 
ordinary effective pressure of such engines ; and to justify this de- 
duction, which, however, is still not enough to harmonize the theore- 
tical and practical results in many circumstances, he is obliged to es- 
timate the friction of the piston, with the losses or waste, at -^ of 
the power, and the force requisite for opening the valves and over- 
coming the friction of the parts of machine, at YoT of that power. 
Reflecting that these numbers express fractions of the gross power of 
the engine, we must readily be convinced that they cannot be cor- 
rect ; for, in supposing the engine had a useful effect of 100 horses, 

* The author here refers to the first edition of ' Tredgold on the Steam-En- 
gine :' in the new edition just published, the algebraic parts are transformed by 
the editor into easy practical rules, accompanied by examples familiarly explain- 
ed for the working engineer. 

37 



290 

which, from the reduction or coefficient employed, supposes a gross 
effect of 200 horses, 12 would be necessary to move the machinery, 
40 to draw the piston, &c. ! The exaggeration is evident. 

Besides, in applying this evaluation of the friction to a locomotive 
engine, which is also a high pressure steam-engine, and supposing it 
to have 2 cylinders of 12 inches diameter, and to work at 75 lbs. 
total pressure, which amounts to 60 lbs. effective pressure, per square 
inch, we find that from the preceding estimate, the force necessary to 
draw the piston would be 5650 lbs., whereas our own experiments on 
the locomotive engine, the Atlas, which is of these dimensions, and 
works at that pressure, demonstrate that the force necessary to move, 
not only the two pistons, but all the rest of the machinery, including 
the waste, &c, is but 48 lbs. applied to the wheel, or 2831bs. applied 
on the piston. 

It is then impossible to admit, that in steam-engines the friction 
and losses can absorb the half, nor the third, much less the f of the 
total power developed ; and yet there do occur cases wherein, to re- 
concile the practical effects with the theoretical ones thus calculated, 
it would be necessary to reduce the latter to the fourth part, and even 
to less ; and, what is more, it often happens that the same engine 
which in one case requires a reduction of -f, will not in other cases 
need a reduction of more than about -J-. This is observed in calcu- 
lating the effects of locomotive engines at very great velocities, and 
afterwards at very small ones. 

There is no doubt, then, that the difference observed between the 
theoretical effect of an engine and the work which it really performs, 
does not arise from so considerable a part of the applied force being 
absorbed by friction and losses, but rather from the error of calculating 
in this manner the theoretical effect of the machine. In effect, this 
calculation supposes that the motive force, that is, the pressure of the 
steam against the piston or in the cylinder, is the same as the pres- 
sure of the steam in the boiler ; whereas we shall presently see, that 
the pressure in the cylinder may be sometimes equal to that of the 
boiler, sometimes not the half nor even the third of it, and that it 
depends on the resistance overcome by the engine. 

§ 3. Formulae proposed by divers authors to determine the velocity 
of the piston under a given load, and proofs of their inexactitude. — 
We have said that this problem was net resolved by the foregoing 
method. The following are the attempts made to that end by ano- 
ther way. Tredgold, in his Treatise on Steam-Engines (art. 127 



291 

and following), undertakes to calculate the velocity of the piston from 
considerations deduced from the velocity of the flowing of a gas, 
supposed under a pressure equal to that of the boiler, into a gas sup- 
posed at the pressure of the resistance. He concludes from thence, 
that the velocity of the piston would be expressed by this formula, 

V = 6-5 Vh, 

in which V is the velocity in feet per second, and h stands for the 
difference between the heights of two homogeneous columns of vapour, 
one representing the pressure in the boiler, the other that of the resis- 
tance. But it is easily seen that this calculation supposes the boiler 
filled with an inexhaustible quantity of vapour, since the effluent gas is 
supposed to rush into the other with all the velocity it is susceptible of 
acquiring, in consequence of the difference of pressure. Now, such an 
effect cannot be produced, unless the boiler be capable of supplying the 
expenditure, however enormous it might be. This amounts, conse- 
quently, to supposing that the production of steam in the boiler is 
unlimited. But, in reality, this is far from being the case. It is 
evident that the velocity of the piston will soon be limited by the 
quantity of steam producible by the boiler in a minute. If that pro- 
duction suffice to fill the cylinder 200 times in a minute, there will 
be 200 strokes of the piston per minute; if it suffice to fill it 300 
times, there will be 300 strokes. It is then the vaporization of the 
boiler which must regulate the velocity, and no calculation which shall 
exclude that element can possibly lead to the true result ; consequent- 
ly the preceding formula cannot be exact. 

This is why, in applying this formula to the case of an ordinary lo- 
comotive engine of the Liverpool Railway with a train of 100 tons, 
the velocity the engine ought to assume is found to be 734 feet per 
second, instead of twenty miles an hour, or five feet per second, which 
is its real velocity. 

Again, in his Treatise on Railways (page S3), Tredgold proposes 
the following formula, without in any way founding it on reasoning 
or on fact : 

vie 

V = 240— , 

in which V is the velocity of the piston in feet per minute, I the 
stroke of the piston, P the effective pressure of the steam in the boil- 
er, and W the resistance of the load. But as this formula makes no 
mention either of the diameter of the cylinder, or of the quantity of 
steam supplied by the boiler in a minute, it clearly cannot give the 



292 

■Velocity sought ; for if it could, the velocity of an engine would be 
the same with a cylinder of one foot diameter as with a cylinder of 
four feet, which expends sixteen times as much steam. The area of 
heating surface, or the vaporization of the boiler, would be equally in- 
different : an engine would not move quicker with a boiler vaporizing 
a cubic foot of water per minute, than with one that should vaporize 
but -J- or -j^g-. Hence this formula is without basis. 

Wood, in his Treatise on Railways (page 351), proposes the fol- 
lowing formula also, without discussion, 

where V is the velocity of the piston in feet per minute, I the length 
of stroke of the piston, W the resistance of the load, and P the sur- 
plus of the pressure in the boiler, over and above what is necessary 
to balance the load W. This formula being liable to the same 
objections as the preceding, is also demonstrated inadmissible apriori. 

Consequently, of the three fundamental problems of the calculation 
of steam-engines, two have received inaccurate solutions by means of 
the coefficients, and the third, as we have just seen, has received no 
solution at all. 

§ 4. Succinct exposition of the proposed theory. — After having 
made known the present state of science, with regard to the theory 
and estimation of the effective power of steam-engines, it remains to 
exhibit the theory we apply to them ourselves. 

It is well known, that in every machine, when the effort of the 
motive power becomes superior to the resistance, a slow motion is 
created, which quickens by degrees till the machine has attained a 
certain velocity, beyond which it does not go, the motive power being 
incapable of producing greater velocity with the mass it has to move. 
Once this point attained, which requires but a very short space of 
time, the velocity continues the same, and the motion remains uni- 
form as long as the effort lasts. It is from this point only that the 
effects of engines begin to be reckoned, because they are never em- 
ployed but in that state of uniform motion ; and it is with reason that 
the few minutes, during which the velocity regulates itself, and the 
transitory effects which take place before the uniform velocity is ac- 
quired, are neglected. 

Now, in an engine arrived at uniform motion, the force applied by 
the motive power forms strictly an equilibrium with the resistance ; 
for if that force were greater or less, the motion would be accelerated 



293 

or retarded, which is contrary to the hypothesis. In a steam-engine 
the force applied by the motive agent is nothing more than the pres- 
sure of the steam against the piston, or in the cylinder. The pressure 
therefore in the cylinder is strictly equal to the resistance of the load 
against the piston. 

Consequently the steam, in passing from the boiler to the cylinder, 
may change its pressure, and assume that which is represented by 
the resistance of the piston. This fact alone exposes all the theory 
of the steam-engine, and in a manner lays its play open. 

From what has been said, the force applied on the piston, or the 
pressure of the steam in the cylinder, is therefore strictly regulated by 
the resistance of the load against the piston. Consequently calling 
P' the pressure of the steam in the cylinder and R the resistance of 
the load against the piston, we have as a first analogy, 

P' = R. 

To obtain a second relation between the data and the quresita of 
the problem, we shall observe that there is a necessary equality be- 
tween the quantity of steam produced, and the quantity expended by 
the machine ; the proposition is self-evident. Now, if we express 
by S the volume of water vaporized in the boiler per minute, and ef- 
fectively transmitted to the cylinder, and by m the ratio of the volume 
of the steam generated under the pressure P of the boiler, to the 
volume of water which produced it, it is clear that 

iijS 
will be the volume of steam formed per minute in the boiler. This 
steam passes into the cylinder, and there assumes the pressure P' ; but 
if we suppose that, in this motion, the steam preserves its tempera- 
ture in passing from the boiler to the cylinder, or from the pressure P 
to the pressure P', its volume increases in the inverse ratio of the 
pressures. Thus the volume m S of steam furnished per minute by 
the boiler will, when transmitted to the cylinder, become 

P 

On another hand, v being the velocity of the piston, and a the 
area of the cylinder, a v will be the volume of steam expended by the 
cylinder in a minute. Wherefore, by reason of the equality which 
necessarily exists between the production of the steam and the expen- 
diture, we shall have the analogy of 

P 

a v = m S ,. =r, ; 



294 

which is the second relation sought. 

Consequently, by exterminating P' from the two equations, we shall 
have as a definitive analytic relation among the different data of the 
problem : 

m S P 

a ' R" 

This relation is very simple, and suffices for the solution of all 
questions regarding the determination of the effects or the proportions 
of steam-engines. As we shall develope its terms hereafter, in taking 
it up in a more general manner, we content ourselves to leave it for 
the present under this form, which will render the discussion of it 
easier and clearer. 

The preceding equation gives us the velocity assumed by the pis- 
ton of an engine under a given resistance R. If, on the contrary, 
the velocity of the motion be known, and it be required to calculate 
what resistance the engine will move at that velocity, it will suffice 
to resolve the same equation with reference to R, which will give 

R _ w SP 
a v 

Finally, supposing the velocity and the load to be given before- 
hand, and that it be desired to know what vaporization the boiler 
should have to set the given load in motion at the prescribed velocity, 
it will still suffice to draw from that analogy the value of S, which 

will be 

q _ a v R 



On these three determinations we rest for the moment, because, as 
will soon appear, they form the basis of all the problems that can be 
proposed on steam-engines. 

§ 5. New proofs of the exactitude of this theory, and of the inac- 
curacy of the ordinary mode of calculation. — The theory just develop- 
ed demonstrates that the steam may be generated in the boiler at a 
certain pressure P, but that in passing to the cylinder it necessarily 
assumes the pressure R, strictly determined by the resistance to the 
piston, whatever the pressure in the boiler may be. Consequently, 
according to the intensity of that resistance, the pressure in the cy- 
linder, far from being equal to that in the boiler, or from differing 
from it in a certain constant ratio, may at times be equal to it, and 
at other times very considerably different. Hence those who, in per- 
forming the ordinary calculation, consider the force applied on the 



295 

piston as indicated by the pressure in the boiler, begin by introduc- 
ing into their calculation an error altogether independent of the real 
losses to which the engine is liable. To this cause, then, and not 
to the friction and losses, which can form but the smallest part of it, 
must be attributed the enormous difference which, in this mode of 
calculation, is found between the theoretical effect of the engine, and 
the work which it really executes. 

We have already proved the mode of action of the steam in the cy- 
linder by the consideration of uniform motion ; but in examining 
what passes in the engine, we shall immediately find many other 
proofs. 

1st. The steam, in effect, being produced at a certain degree of 
pressure in the boiler, passes into the tube of communication, and 
thence into the cylinder. It first dilates, because the area of the cy- 
linder is from ten to twenty-five times that of the tube ; but it would 
promptly rise to the same degree as in the boiler, were the piston im- 
moveable. But as the piston, on the contrary, opposes only a cer- 
tain resistance, determined by the load sustained by the engine, it 
will yield as soon as the elastic force of the steam in the cylinder 
shall have attained that point. The piston, in consequence, will be 
a valve to the cylinder. Hence the pressure in the cylinder can 
never exceed the resistance of the piston, for that would be supposing 
a vessel full of steam, in which the pressure of the steam would be 
greater than that of the safety valve. 

2nd. Were it true that the steam flowed into the cylinder, either 
at the pressure of the boiler, or at any other pressure which were to 
that of the boiler in any fixed ratio, as the quantity of steam generat- 
ed per minute in the boiler would then flow at an identical pressure 
in all cases, and would consequently fill the cylinder an identical 
number of times per minute ; it would follow, that as long as the en- 
gine should work with the same pressure in the boiler, it would as- 
sume the same velocity with all loads. Now, we know that precisely 
the contrary takes place, the velocity increasing when the load dimin- 
ishes ; and the reason of it is, that when the load is half, the steam 
flowing also at a half pressure into the cylinder, and consequently 
acquiring a volume double what it had before, will serve for double 
the number of strokes of the piston. 

3rd. Applying the same reasoning inversely, we perceive that 
were the pressure in the cylinder really bearing a constant ratio to 
that in the boiler, or if it be preferred, constant so long as that in the 



296 

boiler did not vary, we. should, in calculating the effort of which the 
engine would be capable, always find it the same, whatever be the velo- 
city of the piston. Thus, at any velocity whatever, the engine would 
always be capable of drawing the same load ; which experience again 
contradicts, for the greater the velocity of the piston, the lower the 
pressure of the steam in the cylinder, whence results, that the load 
of the engine lessens at the same time. 

4th. Another no less evident proof of this is easily adduced. Were it 
true that the pressure in the cylinder were to that in the boiler in any 
fixed proportion, since the same locomotive engine always requires 
the same number of revolutions of the wheel, or the same number of 
strokes of the piston to traverse the same distance, it would follow that, 
as long as those engines worked at the same pressure, they would 
consume in all cases the same quantity of water for the same distance. 
Now, the quantity of water, far from remaining constant, decreases 
on the contrary with the load, as may be seen by the experiments we 
have published on this subject. Here therefore again it is proved, 
that, notwithstanding the equality of pressure in the boiler, the densi- 
ty of the steam expended follows the intensity of the resistance, that 
is to say, the pressure in the cylinder is regulated by that resistance. 

5th. Similarly, the consumption of fuel being in proportion to the 
vaporization effected, it would follow, if the ordinary theory were ex- 
act, that the quantity of fuel consumed by a given locomotive, for the 
same distance, would always be the same, with whatever load. Now 
we again find by experience that the quantity of fuel diminishes with 
the load, conformably to the explanation we have given of the effects 
of the steam in the engine. 

6th. It is again clear, that if the pressure in the cylinder were, as 
it is believed, constant for a given pressure in the boiler, that so soon 
as it was recognised that an engine could draw a certain load with a 
certain pressure, and communicate to it a uniform motion, it would 
follow that the same engine could never draw a less load with the 
same pressure, without communicating to it a velocity indefinitely 
accelerated § since the power, having been found equal to the resis- 
tance of the first load, would necessarily be superior to that of the 
second. Now, experience proves, uiat in the second case the veloci- 
ty is greater, but that the motion is no less uniform than in the first ; 
and the reason of this is, that though the steam may indeed be pro- 
duced in the boiler at a greater or less pressure, and that it matters 
little, yet on passing into the cylinder, it always assumes the pressure 



297 

of the resistance, whence results that the motion must remain uni- 
form as before. 

7th. Finally, in looking over our experiments on locomotives, it 
will be seen that the same engine will sometimes draw a light load 
with a very high pressure in the boiler, and sometimes a heavy load 
with a very low pressure. It is then impossible to admit, as the ordi- 
nary calculation supposes, that any fixed ratio whatever has existed 
between the two pressures. Moreover, the effect just cited is easy to 
explain, for it depends simply on this, that in both cases the pressure 
in the boiler was superior to the resistance on the piston ; and it 
needed no more for the steam, generated at that pressure or at any 
other, satisfying merely that condition, to pass into the cylinder and 
assume the pressure of the resistance. 

It is then visible, from these various proofs, that the pressure in the 
cylinder is strictly regulated by the resistance on the piston, and by 
nothing else ; and that any method like that of the coefficients in the 
ordinary calculation, which tends to establish a fixed ratio between the 
pressure in the cylinder and that of the boiler, must necessarily be 
inexact. 

§ 6. Verification of the two modes of calculation by particular ex- 
amples. — We have sufficiently demonstrated the want of basis of the 
ordinary calculation ; but as the inaccuracy we have just exposed in 
that method might by some be supposed to be of slight importance, 
and they might conceive that, in practical examples, it amounted to 
the obtaining of results, which, if not quite exact, were at least very 
near the truth, we will now attempt to apply it to some particular 
cases. 

The coefficient of reduction for high pressure engines, working 
without expansion and without condensation, not being given by the 
authors who have treated on these subjects, we propose, in order to 
determine it, the two following facts, which took place before our 
eyes :— 

I. The Leeds locomotive engine, which has two cylinders eleven 
inches in diameter, stroke of the piston sixteen inches, wheel five 
feet in diameter, drew a load of 88-34 tons, in ascending a plane in- 
clined 1 in 1300, at the velocity of 20-34 miles an hour ; the effective 
pressure in the boiler being 54 lbs. per square inch, or the total pres- 
sure 68-71 lbs. per square inch. 

II. The same day, the same engine drew a load of 3S-52 tons in 
descending a plane inclined 1 in 1094, at the velocity of 29-09 ; the 



298 

pressure in the boiler being precisely the same as in the preceding 
trial, and the regulator open to the same degree. These experiments 
may be seen in pages 233 and 234 of our Treatise on Locomotives. 

If on one hand be reckoned, according to the ordinary method, 
the theoretic effort applied to the piston, and on the other hand the 
effect really produced, viz., the resistance opposed by the load phis 
that of the air against the train, we find, on referring the pressure and 
the area of the pistons to the foot square : — 

1st case. — Theoretic effort applied on the piston, ac- 
cording to the ordinary calculation l*32x 

(68-71x144) 13,060 lbs. 

Real effect ; . 8,846 



Coefficient of correction ... 0.6S 



2nd case. — Theoretic effort, the same as above . . 13,C60 
Real effect 6,473 



Coefficient of correction . . . 0.50 

The mean coefficient, to apply to the total pressure, to convert the 
theoretic effects to the practical, is then '59. 

We find, then, three very different coefficients : choose the first 
case, then an error occurs in the second ; choose the second, and an 
error must arise in the first ; by taking the third, you will only divide 
the error between the two. In every way an error is inevitable, and 
that alone suffices to prove that every method, like the ordinary one, 
which consists in the use of a constant coefficient, is necessarily in- 
exact, whatever be the coefficient chosen, and to whatever engine the 
application be made ; for it is evident that tne same fact would occur 
in every kind of steam-engine. Only that it might be less marked, 
if the velocities at which the engine were taken were less different ; 
and this is what has hitherto prevented the error of this method from 
being perceived, for all the engines of the same system being imita- 
ted from each other, and moving nearly at the same velocity, the 
same coefficient of correction seems tolerably to suit them, from the 
factitious limit that had been laid down for the speed of the piston. 

Besides, in stationary engines one cannot, for want of precise de- 
terminations of the friction, disengage in the result the part which is 
really attributable to it from that which constitutes a positive error. 



299 

But here we may easily be convinced that neither of these coefficients 
of correction represents, as the ordinary theory would have it, the 
friction, losses, and various resistances of the machine ; for direct 
experiments made on the engine under consideration, and noted in 
our Treatise on Locomotives, enable us to estimate separately all 
these frictions, losses, and r - esi stances. Reckoning, then, the fric- 
tion of the engine at 82lbs., taking account besides of its additional 
friction per ton of load, and adding for each case the pressure sub- 
sisting on the opposite side of the piston by the effect of the blast 
pipe, we find, as the sum of the friction and indirect resistances — 

1st case. — Friction ■ 1,257 lbs. 

or «10 of the theoretic result. 
2nd case. — Friction S73 lbs. 

or -07 of the theoretic result. 

Thus we see, that in each of the two cases, the friction and indirect 
resistances, omitted in the calculation, do not in reality amount to 
more than 10 or 7 hundredths of the theoretic result ; and if we should 
be disposed to add to that t/- - or -05, for the filling of the vacant spaces 
of the cylinder, which we could not estimate in lbs., it will be -15 and 
•12; whereas the coefficients of correction would raise them to -32 
in one case, and -50 in the other ; that is, to 2 and 4 times what they 
really are. If, then, from these coefficients, be deducted the true value 
of the friction and losses, it will appear that the theoretic error, intro- 
duced into calculation under the denomination of friction, is 17 per 
cent, of the total power of the engine in the one case, and 38 per 
cent, in the other. 

But it is to be remarked, that, from the preceding evaluations, viz., 
of the direct resistances first, and then of the friction and indirect re- 
sistances, we' have, for each of the two cases in question, the sum of 
the total effects really produced by the machine as follows : — 

1st case. — Direct resistances 8,846 lbs. 

Friction 1,257 



10,103 



2nd case. — Direct resistances ..... 5,473 
Friction « ■ i 873 

6,346 



300 



We are therefore enabled now to compare these effects produced 
with the results either of the ordinary calculation or of our theory. 

1°. In applying the ordinary calculation with the mean coefficient 
•56 determined above, and comparing its result with the real effect, 
we find — 
1st case. — Effort applied on the piston, according to the 

ordinary calculation, 1-32 x (68-71 x 144) x '59 7,705 lbs. 
Effect produced, including friction and every resis- 
tance ....... 10,103 

Error over and above the friction and resistances 2,398 



2nd case. — Effort applied on the piston, according to 

the ordinary calculation, the same as above . 7,705 lbs. 
Effect produced, including friction and every resis- 
tance , , 7,346 



Error over and above the friction and resistances . 359 

Mean error of the two cases 1,37S 

It is then evident what error would have been committed in calcu- 
lating the effects of this engine from the coefficient -59 ; but it is 
equally evident, that in applying any other coefficient whatever, the 
error would only transfer itself from one case to the other, without 
ever disappearing ; and thus it is that the coefficient, -59 has almost 
annulled the error of the second case, by transferring it to the first. 
To apply our formula with reference to the same problem, viz. : — 

a R= . , 



a v 
we have nothing more to do than to substitute for the letters their 
value, taking care to refer all the measures to the same unit. In 
making then these substitutions, which give P = 68-71 x 144 lbs., 
m = 411, a = 1-32, and observing that the effective vaporization of the 
engine has been S = -77 cubic foot of water per minute, we find, — 
1st case. — Effort applied by the engine at the given velo- 
city, according to our 

41 1 x 0-77 X (68-71 X 144) 
theory, -| - y . . . 10,507 lbs. 

Effect produced, including friction and resistances, 

as above f . . . 10,103 

Pifference ....,...,.«. 404 



301 

2nd case. — Effort applied by the engine at the given ve- 
locity, according to our 

. 411 x 0-77 X (68-71 x 144) 
theory, -±- '- .... 7,215 lbs. 

Effect produced, including friction, &c 7,346 



Difference 131 

Mean difference of two cases 267 

It appears, then, that by this method, the useful effect is found with 
a difference only of 267 lbs., a very inconsiderable difference in 
experiments of this kind, wherein so much depends on the manage- 
ment of the fire. 

2°. To continue the same comparison of the two theories, let it 
be required to calculate what quantity of water per minute the boiler 
ought to vaporize, to produce either the first effect or the second. 
The method followed by the ordinary theory, again consists in pre- 
viously supposing that the volume described by the piston has been 
filled with steam at the same pressure as in the boiler, and then in 
applying to it a fractional coefficient to account for the losses. 

Now, in the first case, the volume described by the piston at the 
given velocity, is 1 '32x298= 393 cubic feet. Had this volume been 
filled with steam at the pressure of the boiler, it would have required 

393 . 

a vaporization of — - = -96 cubic foot of water per minute. But the 

real vaporization was but -77 ; wherefore, in the first case, the coef- 
ficient necessary to lead from the vaporization indicated by the ordi- 

' "77 
narv calculation, to the real vaporization, j—= '81. 

In the second case, we find in the same manner, that the coeffi- 
cient should be -55 ; whence, in this problem, as in the preceding 
one, no constant coefficient whatever can suffice. 

Performing, however, the calculation with the mean coefficient, 
•68, we find, — 

1st case. — Vaporization per minute, calculated by the ordinary 

1-32 X 29S 
theory, with the coefficient, — — X *68 . . . -65 

Real vaporization ,,....« -77 

Error , . * ,.,..,. '12 



302 



2nd case. — Vaporization per minute, calculated by the ordinary 

., , 1-32 X 434 

theory, with the coefficient, X '6S . . . *95 

411 

Real vaporization -77 



Error -IS 

The mean error committed is then \ of the vaporization, and be- 
ing, as it is, a mean, it may, in extreme cases, become f, or amount 
to half of the whole vaporization. 

This is the error committed in seeking a coefficient expressly for 
the vaporization. Bnt when the coefficient, determined in the pre- 
ceding case, that is, by the comparison of the theoretical and practical 
effects, is used as a divisor, as by many authors it is, much greater 
errors are induced, which we will show by an example farther on. 

In our theory, on the contrary, the vaporization necessary to set in 
motion the resistance a R at the velocity v, is given by the formula 

c a R x v 

We have then, — 
1st case. — Vaporization calculated from our 
10103X298 

the0 ^4UX (68-71X144) ' ' 74 

Real vaporization -77 

Difference -03 

2nd case. — Vaporization calculated from our 
7346 X 434 

the ° r *"' 411 X (68-71 X 144) * 7S 

Real vaporization -77 

Difference -01 

3°. Lastly, in the case of finding the velocity of the piston, sup- 
posing the resistance to be given, any method similar to the ordinary 
one must inevitably lead to errors ; but we must dispense with com- 
parison, since this problem has never been resolved, and we shall 
therefore in this case merely show the verification of our own theory. 
The formula relative to this problem is 

roSP 
v = . 



303 

We find then, — 
1st case. — Velocity of the piston in feet per minute, calcu- 

/, r 4 , 411 x '77 X (68-71 X 144) 

ted from our theory, , , ■■ . . 310 

■" lulo3 

Real velocity 298 



411 x ■"< 


H X (68-71 x 144) 


,ry ' lul03 








.... 



Difference 12 



2nd case. — Velocity of the piston from our 

iU 411 x '77 X (68-71X144) 
theory, ^ 

Real velocity 434 



411 X '77 X (68-71x144) 
theory, ^^ ...... 426 



Difference 



It consequently appears, that in each of the Ihree problems in 
question, our theory leads to the true result ; whereas the ordinary 
theory, besides that it leaves the third problem unresolved, may, in 
the other two, lead to very serious errors. 

Before abandoning this comparison, we request attention to an 
effect, in calculating by the ordinary theory, which we have already 
mentioned, but which is here demonstrated, viz., that this calculation 
gives the same force applied by the engine in both the cases consi- 
dered, notwithstanding their difference of velocity: and such will 
always be the result, since the calculation consists merely in multi- 
plying the area of the piston by the pressure in the boiler, and reduc- 
ing the product in a constant proportion. This theory therefore 
maintains, in principle, that the engine can always draw the same 
load at all imaginable velocities. Again we see, that, in the same 
calculation of the load or effort applied, the vaporization of the en- 
gine does not appear, which would imply that the engine would 
always draw the same load at all velocities, whatever might be the 
vaporization of the boiler, which is inadmissible. 

We shall also remark, that in calculating by the ordinary theory 
the vaporization of the engine, no notice is taken of the resistance 
which the engine is supposed to move ; so that the vaporization ne- 
cessary to draw a given load would be independent of that load — 
another result equally impossible. 

To these omissions, therefore, or rather to these errors in princi- 
ple, are to be attributed the variations observable in the results given 
of the ordinary theory in the examples proposed. 



304 



PART II 



ANALYTIC THEORY OF THE STEAM-ENGINE. 

ARTICLE. I. 

fcASE OF A GIVEN EXPANSION WITH ANY VELOCITY OR LOAD 

WHATEVER. 

§ 1. Of the change of temperature of the steam during its action 
in the engine. — When an engine is at work, the steam is generated 
in the boiler at a certain pressure ; it passes from thence into the cy- 
linder, assuming a different pressure, and, in an expansive engine, 
the steam, after its separation from the boiler, continues to dilate it- 
self more and more in the cylinder, till the piston is at the end of the 
stroke. It is generally supposed, that in all the changes of pressure 
which the steam may undergo, its temperature remains the same ; and 
it is consequently concluded, that during the action of the steam in 
the engine, the density and volume of that steam follow the law of 
Mariotte, namely, that its volume varies in the inverse ratio of the 
presure. This supposition greatly simplifies the formuke ; but, as 
reason and experience prove it to be altogether inexact, we are com- 
pelled to renounce it, and will substitute in its place another law, de- 
duced from observation of the facts themselves. 

We have recognised in a numerous series of experiments, by ap- 
plying simultaneously a manometer and a thermometer, both to the 
boiler of a steam-engine, and also to the tube through which the 
steam, after having terminated its effect, escaped into the atmos- 
phere, that during all its action in the engine the steam remains in 
the state denoted by the name of saturated steam, that is, ; at the max- 
imum density for its temperature. The steam, in fact, was produced 
in the boiler at a very high pressure, and escaped from the engine 
at a very low one ; but on its issuing forth, as well as at the moment of 
its formation, the thermometer indicated the temperature correspond- 



ing to the pressure marked by the manoinetef, as if the steam were 
immediately generated at the pressure it had at that moment. 

Thus during its whole action in the engine, the steam remains 
constantly at the maximum density for its temperature. 

Now, in all steams, the volume depends at once on the pressure and 
the temperature ; but in the steam at the maximum density, the tem- 
perature itself depends on the pressure. It should then be possible 
to express the volume of steam of maximum density, in terms of the 
pressure alone. 

The equation which gives the volume of the steam in any state 
whatever, in terms of the pressure and temperature, is very simple : 
it is deduced from Mariotte's law combined with that of M. Gay- 
Lussac. The equation which gives the temperature in terms of the 
pressure, for the steam at the maximum density, is also known : it 
has been deduced from the fine experiments of Messrs. Arago and 
Dulong on steam at high pressures, and from those of Southern and 
other experimenters on steam produced under low pressures. By 
eliminating then the temperature in these two equations, we shall 
obtain the analogy required, which will give immediately, with re- 
gard to steam at the maximum density, for its temperature, the vo- 
lume in terms of the pressure alone. 

But here arises the difficulty. The equation of the temperatures 
is not invariable ; or rather, the same equation does not apply to all 
points of the scale. To be used with accuracy, it requires to be 
changed according as the pressure is under that of one atmosphere, 
or comprised between one and four atmospheres, or again if it be 
above four atmospheres. Now, when steam is acting in an engine, 
it may happen, according to the load, or to other conditions of its 
motion, that the steam generated at first at a very high pressure, may 
act or be expanded in the engine sometimes at a pressure exceeding 
four atmospheres, sometimes at a pressure less than four atmospheres, 
but yet exceeding one, and sometimes at a pressure under that of one 
atmosphere. It is impossible then to know which of the three for- 
mulae is to be used in the elimination ; and consequently it is impossi- 
ble by this means to attain a general formula representing the effects 
of the engine in. all cases. 

Moreover, were either one of these formulae adopted, the high 
radical quantities they contain would so complicate the calculations 
as to render them unfit for practical purposes. And it is to be re- 
marked, that these divers formulae, after all, are not the expression of 

39 



306 

the true mathematical law which connects the temperature and the 
pressure in saturated steam, but merely empirical relations, which ex- 
periment alone has demonstrated to have a greater or less degree of 
approximation. 

A formula of temperatures given by M. Biot is indeed adapted to 
all points of the scale, and may be useful in a great number of deli- 
cate researches relative to the effects of steam ; but as it gives only 
the pressure in terms of the temperature, and is, from its form, inca- 
pable of the inverse solution, namely, the general determination of 
temperatures in terms of the pressure, it is unfit for the elimination 
proposed. 

Under these circumstances the only resource is to seek a direct 
relation in terms of the pressure alone, whose results shall represent 
immediately those of the two preceding formulae combined - r that is, 
to calculate first by means of those formulae a table of volumes of the 
steam, and then to seek a direct and simple relation to represent those 
results. This we have done. 

M. Navier had proposed a formula for this purpose. But that for- 
mula, though sufficiently exact in high pressures, differs widely from 
experience in pressures below that of the atmosphere, which are useful 
in condensing engines ; and it is possible to find one much more 
exact for non-condensing engines, namely, that we are about to offer. 
We propose then, for this purpose, the following formulae, in which p 
represents the pressure of the steam expressed in pounds per square 
foot, and /x the ratio of the volume of the steam to that occupied by 
the same weight of water : 

Formula for high or low k 10000 

pressure engines ivith 



"condensation' " i ' °' 4227 + °-0Q258p 

Formula for high press- \ 10000 



ure non-condensing en- 



gines ° j " 1-421 +0-0023P 

The first formula is equally suitable to pressures above and below 
that of the atmosphere, at least within the limits likely to be consi- 
dered in applying it to condensing steam-engines. Those limits are 
eight or ten atmospheres for the highest pressures ; and eight or ten 
pounds per square inch for the lowest, in consequence of the friction 
of the engine, the pressure subsisting against the piston after imper- 
fect condensation in the cylinder, and the resistance of the load. 



307 

Within these limits then the proposed formula will be found to give 
very approximate results. 

This first formula might also be applied, without any error worthy 
of notice, to non-condensing engines. But as, in these, the steam 
can scarcely operate with a pressure less than two atmopheres, by rea- 
son of the friction of the engines and the resistance of the load, it 
is needless to require of the formula exact results of volumes for pres- 
sures under two atmospheres. 

In this case then the second formula will be found to give those 
results with much greater accuracy, and will consequently be preferred 
in practice. This will be readily recognised in a table annexed to 
the work, presenting a comparison of the volume of the steam calcu- 
lated by the ordinary formulae in terms of the pressure and tempera- 
ture, and by the proposed formulaB in terms of the pressure alone. 

We state then generally this analogy : 

y- = — j .... (a) 

n-\~qp ' 

Consequently, if the steam pass in the engine, from a certain 
volume m to another known volume in, and thereby abandon its 
primitive pressure P', to assume an unknown pressure p, it is easy 
to recognise that the following relation will exist between those two 
pressures, and will serve to determine the unknown quantity p, viz. : 
p m 1 — n )i 
P' /i " 1 — niri' 

This is the relation which we substitute in lieu of that hitherto em- 

ployed, and according to which the volume appears to vary in the 

inverse ratio of the pressure. It will be observed that such an hypo- 

thesis may be deduced from the analogy we have just offered, by 

mP 
making n = 0, and q = , m being the volume, and P the pressure 

of the steam in the boiler ; for it is plain that we shall then have, 

ii»P 

n — , 

P 
that is to say, the volumes are inversely as the pressures. 

§ 2. Of the divers problems xvhich present themselves in the calcu- 
lation of steam-engines. — We distinguish three cases in an engine : 
that wherein it works with a given rate of expansion of the steam, 
and with a load or a velocity indefinite ; that in which it works with 
a given rate of expansion, and with the load and velocity proper to 



30S 

produce its maximum of useful effect with that expansion ; and lastly, 
that wherein, the engine having been previously regulated for the 
expansion of the steam most favourable in that engine, it bears, more- 
over, the load most advantageous for that expansion ; which, conse- 
quently, produces -the absolute maximum of useful effect in the 
engine. 

We have said that the three fundamental problems of the calculation 
of steam-engines consist in finding successively the velocity, the 
load, and the vaporization of the engine. 4fter the solution of these 
three problems, that which first presents itself, as a corollary to them, 
consists in determining the useful effect of the engine, which may be 
expressed under six different forms, viz. : by the work done, or the 
number of pounds raised one foot high by the engine in a minute ; 
by the horse power of the engine ; by the actual duty or useful effect 
of one pound of coal ; by the useful effect of a cubic foot of water 
converted into steam ; and by the number of pounds of coal, or of 
cubic feet of water, that are necessary to produce one horse power. 

Another research, in fine, no less important, is the rate of expan- 
sion at which the steam must work in an engine, in order that it may 
produce given effects. We shall present successively the solution of 
all these questions. 

The various problems will be resolved in each of the three cases 
above mentioned. In the two last, the question will be to calculate 
the rate of expansion, the velocity, the load, and the effects which cor- 
respond to the maximum of, relative or absolute, useful effect of the 
engine. 

In the ordinary calculations of steam-engines, the solution of three 
questions only had been attempted, viz., — to find the load, the vapo- 
rization, and the useful effect, under its different forms ; which solu- 
tion is, as we have seen, faulty. As to the determining of the velo- 
city for a given load, and that of the rate of expansion for given ef- 
fects, the calculation of these had not been proposed. Moreover, 
the very nature of the theory employed in those calculations did not 
allow of distinguishing, in the machine, the existence of the three 
cases which are really found in it. The distinction we establish 
may, therefore, at first appear obscure, expressed, as it is, in general 
terms, and including relations unusual in the consideration of steam- 
engines ; but, on a closer view of the question, these relations will 
be seen to be of indispensable necessity, in order to calculate with 



309 

exactitude either the effects or the proportions of steam-engines of 
all systems. 

§ 3. Of the velocity of the piston under a given load. — To em- 
brace at once the most complete mode of action of the steam, we will 
suppose an engine working by expansion, by condensation, and with 
an indefinite pressure in the boiler ; and to pass on to unexpansive 
or uncondensing engines, it will suffice to make the proper suppres- 
sions or substitutions in the general equations. 

From what has been already shown of our theory, the relations 
sought between the various data of the problem are necessarily deduc- 
ed from two general conditions ; the first expressing that the engine 
has attained a uniform motion, and consequently that the quantity of 
labour impressed by the motive power is equal to the quantity of ac- 
tion developed by the resistance : the second, that there is a neces- 
sary equality between the emission of steam through the cylinder and 
the production by the boiler. 

The limits of this extract will not allow us to develop those calcu- 
lations, simple as they may be ; but that the proceeding may be un- 
derstood, we shall state that, expressing by P the pressure of the 
steam in the boiler, and by P' the pressure of the same steam in the 
cylinder before the expansion, by L the length of stroke of the piston, 
and by L' the portion traversed at the moment the expansion begins, 
by a the area of the piston, and by c the clearance of the cylinder, or 
the space at each end of the cylinder beyond the portion traversed by 
the piston, and which necessarily fills with steam at each stroke ; last- 
ly, by r the resistance of the load, by p the pressure subsisting on 
the other side of the piston after imperfect condensation, by f the 
friction of the engine when not loaded, and by S the increase of. that 
friction per unit of the load r, these four forces, as well as the pres- 
sures, being moreover referred to the unit of surface of the piston ; 
the first of the above conditions produces the following analogy : 
P' a (L # + c) c L' L -f c ? 

1=^(17+75 < LH^ + I ° g * i7+c~ na L S = 

ah({l + l)r+p+f) (A) 

This equation expressing that the labour developed by the mover is 
found entire in the effect produced, be it remarked, that it is not es- 
sentially necessary for the motion to be strictly uniform. It may 
equally be composed of equal oscillations, beginning from no velocity, 
and returning to no velocity, provided the change of velocity take 



310 

place by insensible degrees, so as to avoid the loss of vis viva, and 
that the successive oscillations be performed in equal times. 

As to the second condition of the motion ; if we denote by S the 
volume of water vaporized by the boiler in a unit of time and trans- 
mitted to the cylinder, by m the volume of the steam formed under 
the pressure P of the boiler, compared with the volume of the same 
weight of water unvaporized, and by v the velocity of the piston, the 
equality between the production of the steam and its consumption 
will be foupd to furnish the second general analogy : 

S v 
— = -— a (L' + c) (B) 

Consequently, by eliminating P' from these two equations, and 
writing, for greater simplicity, 
L 

— MflL 

L' +c 



L L + c ' 

—. (- log. rr-7— noL 

L 4-c n ° L -fc 

we find definitively : 

L S 1 

V= V~+c' «'» + 9* j {l+t)r+p+f\ 
an equation which gives the velocity of the motion in terms of the 
load and of the other data of the problem. 

This formula is quite general, and suits every kind of steam- 
engine with continued motion. If the engine be expansive, L' will 
be replaced by its value corresponding to the point of the stroke 
where the steam begins to be intercepted ; if the engine be unex- 
pansive, it will suffice to make L' = L, which will give at the same 
time*=l. If it be a condensing engine, p must stand for the 
pressure of condensation ; if it be not a condenser, p will represent 
the atmospheric pressure. And finally, the quantities n and q will 
have, according to the case considered, the above-mentioned value. 

§ 4. Of the load and useful effects of the engine. — If, instead of 
seeking the velocity in terms of the load it be required, on the con- 
trary, to know the load suitable to a given velocity, the same equation 
resolved with reference to r becomes, 

L 

S — nav 
Li + c p -j- f 

ar = — ±— — a 1 —^- s .... 2 

3°. To find the vaporization of which the engine ought to be ca- 



311 

pable, in order to put in motion a resistance r with a known velocity 
v, the value of S must be drawn from the same analogy, thus ; 

» = t±f«'(n + ? .{(i + i)*"+l»+/|) .... (3) 

4°. The useful effect produced by the machine, in the unit of time, 
at the velocity v, is evidently arv. Hence that useful effect will have 
for its measure, 

L 



v L' + c P+f ,., 

uE. = ; CIV ; — : .... (4) 

_ {1+S)q* 1 + 3 _ k ' 

5°. If it be desired to know the useful effect, in horse power, of 
which the engine is capable at the velocity v, or when loaded with the 
resistance r, it suffices to observe that what is called one horse power 
represents an effect of 33,000 lbs. raised one foot per minute. All 
consists then in referring the useful effect produced by the engine in 
a unit of time, to the new unity just chosen, viz. to one horse power ; 
and it will consequently suffice to divide the expression already ob- 
tained in the equation (4) by 33,000. Thus, the useful effect in 
horse power will be, 

uE. 

uHP. = — .... (5) 

33U00 v ; 

6°. We have just expressed, in the two preceding questions, the 

effect of the engine by the work which it is capable of performing. 

We are now on the contrary about to express that effect by the force 

which the engine expends to produce a given quantity of work. The 

useful effect of the equation (4) being that which is due to the volume 

of water S converted into steam, in the unit of time, if we suppose 

that in the same unit of time N pounds of fuel be consumed, it is 

clear that the useful effect produced by each pound of fuel will be the 

Nth part of the above effect. It will then be, 

uE. 
uE. 1 lb. co. = — _- (6) 

To apply this formula, it will suffice to know the quantity of coal 
consumed in the furnace per minute, that is, during the production of 
the vaporization S ; and this datum may be deduced from a direct 
experiment on the engine, or from known experiments on boilers of 
a similar construction. 

7°. The useful effect of the equation (4) being that which proceeds 
from the vaporization of the volume of water S, if it be required to 



312 

know the useful effect that will be produced by each cubic foot of 
water, or by each unit of S, it will be sufficient to divide the total ef- 
fect uE. by the number of units in S. It will then be, 

uE. 
uE. 1 ft. wa. = -— (7) 

8°. In the sixth problem we have obtained the useful effect produ- 
ced by one pound of fueL We may then, by a simple proportion, de- 
duce from thence the quantity of fuel necessary to produce* one horse 
power, viz. 

33000 N 
Q. co. for 1 hp. =— -^ ..... (8) 

9°. And similarly, the quantity or volume of water necessary to 

produce one horsepower will be, 

33000 S 
Q. wa. for 1 hp. = - — (9) 

§ 5. Of the expansion of steam, to be adopted in an expansive en- 
gine, in order to produce wanted effects. 

10°. Finally, if it be required to know what rate of expansion the 
engine must work at, in order to obtain from it determined effects, 
the value of L' must be drawn from equation (1). It will be given 
by the formula, 

v L' + c 

" nav — - — - 

— f7 — \-nah .... (10) 

o *-• + c 

b — nav — — 

Li 

This formula not being of a direct application, we annex to the 
work a table which gives its solutions for the expansion from hun- 
dredth to hundredth, with a very short calculation. 

We confine ourselves to these inquiries as being those which may 
most commonly be wanted ; but it is clear that by means of the same 
general analogies, any one whatever of the other quantities which 
figure in the problem may be determined, as the case may require. 
Thus, for instance, may be determined the area of the piston, or the 
pressure in the boiler, or the pressure in the condenser, correspond- 
ing to determined effects of the machine, as has been done for loco- 
motives in our work on that subject. 



313 



ART. II. 

CASE OF THE MAXIMUM USEFUL EFFECT, WITH A GIVEN RATE 
OF EXPANSION. 

§ 1. Of the velocity of the maximum useful effect. We have resolv- 
ed the above problems in all their generality, that is, supposing the 
engine to move any load whatever with any velocity whatever, under 
this single condition, that the load and the velocity be compatible 
with the capability of the machine. The question is now to find 
what velocity and what load are most advantageous for the working 
of the engine, and what are the effects which, in this case, may be 
expected from it ; that is to say, its maxima effects for a given rate 
of expansion. 

1°. In examining the general expression of the useful effect pro- 
duced by the engine at a given velocity, we perceive that the expres. 
sion attains its maximum for a given rate of expansion when the 
velocity is a minimum ; now from the equation (B) the smallest 
value of 15 will be given by P' = P. The velocity corresponding to 
the maximum useful effect will therefore be, 
S L 

V = ^+TP) ' L'+c ' ' ' ' W 
Let us however remark, that, mathematically speaking, the pressure 
P' of the steam in the cylinder can never be quite equal to P, which 
is the pressure in the boiler ; because there exist between the boiler 
and the cylinder conduits through which the steam has to pass, and 
the passage of these conduits offers a certain resistance to the motion 
of the steam ; whence results that there must exist, on the side of the 
boiler, a trifling surplus of pressure equivalent to the overcoming of 
the obstacle. But as we have proved elsewhere, that, with the usual 
dimensions of engines, this difference of pressure is not appreciable 
by the instruments used to measure the pressure in the boiler, the 
introduction of it into the calculations would render the formulae more 
complicated without making them more exact. For this reason we 
neglect that difference here. 

The velocity given by the preceding equation is, then, that at 
which the engine will produce its maximum effect for a given expan- 
sion. This velocity will result from the condition P' = P, or reci- 
procally, when this velocity takes place in the engine, the steam enters 

40 



314 

the cylinder with full pressure, that is, with the same pressure it has 
in the boiler. It is necessary to remark that the velocity of full pres- 
sure will not be the same for all engines ; on the contrary, it will 
vary in direct ratio with the vaporization, and in the inverse ratio of 
the area of the cylinder. It may then occur to be, in one engine, 
the half or the double of what it would be in another; which shows 
that it is an error to believe that, because the piston of stationary en- 
gines does not in general exceed a certain velocity of from 150 to 
250 English feet per minute, the steam of the boiler necessarily 
reaches the cylinder with no change of pressure. 

It is easy to be seen that a fixed limit, whatever it may be, cannot in 
this respect suit all engines ;' and that the only means of knowing 
the velocity of the maximum effect, or of full pressure of an engine, 
is to calculate it directly for that engine. Such is the object of the 
formula we have just given. This formula, moreover, is of a remark- 
able simplicity, and requires no other experimental knowledge than 
that of the production of steam of which the boiler is capable. 

§ 2. Of the load and maximum useful effect of the engine — 2°. 
The useful resistance which the machine is capable of putting in mo- 
tion at its velocity of the maximum effect above, is to be drawn from 
equation (2), substituting for v the Value just obtained. Calling the 
load r' we shall find it expressed by 

« P P+f 



~(i +<0* i + s ' 

and it is at the same time visible that this load is the greatest the en- 
gine can put in motion with the given expansion L', for it corres- 
ponds to the lowest value of v in equation (2). Thus, the greatest 
effect of the machine, with a given rate of expansion, is attainable 
by working the machine at its smallest velocity and with its maximum 
load. 

It will be observed that this equation may be used to determine 
the friction of the engine without a load, and its additional friction 
per unit of the load, Upon the same principles that we have employed 
in our Treatise of Locomotive Engines for similar determinations. 
This is also the mode we propose for steam-engines of every system. 

3°. The vaporization necessary to an engine, in order to exert a 
certain maximum effort r' at its minimum velocity v', will be given 
by equation (3), by substituting in itr' and v', or will be drawn more 
simply from equation (11), thus :— 



315 

S = (n + qV)ao>.~j^ .... (13) 

4°. The maximum of useful effect producible in the unit of time, 
by an engine working with a given expansion, will be known by for- 
mula (4), by introducing for v the velocity proper to produce that ef- 
fect. Thus is found, 

L S cP „ > 

max. uE. = =-, . ; — \ {p-\-f){ ■ • • • (14) 

It will be observed that this maximum .useful effect depends partic- 
ularly on the quantity of water S, evaporated per minute in the boil- 
er. Hence we see plainly the error of those who pretend to calcu- 
late the useful effect or the power of engines from the area and the 
velocity of the piston, which they set in the place of the vaporization 
produced : this vaporization not only entering not into their calcula- 
tion, but forming no part of their observations. 

5°. The useful effect, in horse power, of the engine will be ex, 

pressed by 

„,, max. uE. 
uHP. =— — — — (15) 

33UU0 v ; 

6°. 7°. 8°. 9°. The various measures of the useful effect will here 
be deduced from equations similar to those (6), (7), (8), and (9). 

10°. The expansion at which the engine ought to be regulated, in 
order to draw a given load at the most advantageous velocity, or pro- 
ducing the maximum of useful effect with that load, will be derived 
from equation (12), which gives, 

L' + c< L' L+c) (i± s ) r +p+f L'-fe 

— =- — — \-na — - — ■ 






L'-fc ' & L' + c 



L _ L (L+i^±£+/| (20) 



and the solutions of this formula will be found immediately, and 
without calculation, by means of the table given above, as suggested 
by equation (10). 



316 



ART. III. 

CASE OF THE AESOLUTE MAXIMUM OP USEFUL EFFECT. 

The preceding inquiries suffice for engines working without ex- 
pansion, merely by making L' = L ; because those engines fall un- 
der the case of expansion fixed a priori. But it is otherwise with 
engines in which the rate of expansion may be varied at will. We 
have seen that, for a given expansion, the most advantageous way 
of working the engine is to give it the maximum load, which is cal- 
culated a priori from equation (12). Hence we know what load is to 
be preferred for every rate of expansion. But the question now is to 
determine, among the various rates of expansion of which the engine 
is susceptible, each accompained by its corresponding load, which 
will produce the greatest useful effect. 

For this purpose we must recur to equation (14), which gives the 
useful effect produced with a maximum load r, and seek among all 
the values assignable to L', that which will raise the useful effect to a 
maximum. Now, by making the differential coefficient of that ex- 
pression, taken with reference to L', equal to nothing, we find as the 
^condition of the maximum sought : 

L -f- c / L\ 

L p +.f T 1 °S'I7+- c -» aL ( 1 -L) 

"Sr^ + naL ft (30) 



L 



nah 



VL' + c 

This equation will be resolved in the same manner as the equa- 
tions (10) and (20), by means of the table already given ; and after 

L' . 

having found the value of — , it will be introduced in the equations of 
J_i 

Article II. ; and the corresponding velocity, load, and useful effects, 

will be determined. 

However, as the supposition of n = o, q = — p, that is to say, 

the supposition that the steam preserves its temperature during its 
action in the engine, will give a sufficient approximation in a great 
pnany cases, we present here the corresponding results of all the for- 



317 



muke. They will show, already to a very near degree, the maximum 
absolute effects which it is possible to obtain from an engine, in 
adopting simultaneously the most advantageous rate of expansion 
and the most advantageous load. 



(21)," = 

(22) ar"=.a 

log. 

(23) S: 



LP 



m S 



« L\p+f) + V 



(1 + <0L 
(L + c)P 



L(p+/) + Pc 
m' LP 



(24) ab.max.u.E: 



-.ar v = 



jbSP 

r+7 



log. 



(25)»-HP = 
(30) L' = 



P (L + c) 
L(jp+/) + Pc 

ab. max. u. g 



33UUU 
L(JP+/) 



Velocity of the absolute maximum 
useful effect. 

Load of the piston corresponding 
to the absolute maximum useful 
effect. 



Vaporization. 



Absolute maximum of useful ef- 
fect. 

Absolute maximum of useful force 
in horse power. 

Rate of expansion which produces 
these effects. 



The four determinations of the useful effects of a given quantity of 
fuel or water will be furnished by equations similar to those (6), (7), 
(8), and (9). 

The only remark we shall make on the subject of these formula? is, 
that the load suitable to the producing of the absolute maximum use- 
ful effect is not the maximum load that may be imposed on the en- 
gine. In effect, from equation (12), we know that the maximum 
load for the engine takes place when L' = L, and not when 

Thus the greatest possible load of the engine is that of the maxi- 
mum useful effect without expansion ; but by applying a lighter load, 
that of equation (22), and at the same time the expansion of equation 
(30), a still greater useful effect will be obtained. 



318 



PART III. 



APPLICATION OF THE FOR.MUL3; TO THE VARIOUS SYSTEMS OF STEAM 

ENGINES. 

We shall not give here the applications to different systems of steam- 
engines, which are developed in this part of the work. We shall 
confine ourselves to what cpncerns Watt's steam-engines, because 
they are the most generally employed in the arts. 

Watt's rotative double-acting steam-engine. — These engines being 
without expansion, the proper formulae for. calculating their effects 
will be deduced from the general formulae by making L' = L, which 
will give also K = 1, and by replacing the quantity p by the pressure 
of condensation. We see, moreover, that for these engines, the ex- 
pansion being susceptible of no variation, since that detent does not 
exist, the third case, considered as to engines in general, cannot oc- 
cur. There will be then but two circumstances to consider in then- 
working, viz., the case wherein they operate with their maximum 
load, or load of greatest useful effect, and the case in which they ope- 
rate with any load whatever. The effects therefore of these engines 
will visibly be determined by the following equations : 



<© 



<© 



£> 



H 



H 



<© 



M 



W 






II 


1! 


1 




1 


1 


II 




CO 




CO 














to 




CO 










CO 


c 


o 


c 


o 




a 




a 


CO 


H 


o 
o 

CO 


k 


o 

o 

3 


CO 


ft] 


tzl 


W 


c 
c 

c 



H 



a 



H 



GO 



a fni 




F 


« « i 


F 


+ 
ft 



+ 



+ 



+ 



§ kO 



5 I CO 



II 



+ 



+ +1 



U5I8 "J- 8 

+ ^ + 






^3 + + 

8 S> 



a 



S 



CO 



H 



CO 


3 

S3 


CO 


CO 


CO 


o 


M 


o 


o 


* 


o 


o 


• 


o 


CO 


W 


3 



DC 



3 



ft 



H 



+ 



p a 



+ 

+ 

(35 

3\ 

hj 
I 

I 



8 

+ 



F i- 


. 


F 


-f + 


a 


+ 


ft o-, 




ft 






hi 


a 


f 




1 


s 


^3 
I 


+ 


1 


sO 




■s 


hj 



f£ 



^ 



GO 



^ 



320 

Athough these formulae may at first sight appear complicated, 
they will nevertheless be found very simple in the calculation. It is 
only necessary to fix attention to refer all the measures to the same 
unit, as will be seen in the following example. It must be remarked 
also, that as soon as the velocity and load of the engine are determin- 
ed, the useful effect will be known immediately, being their produce. 

To apply, however, these formulas, some previous observations are 
necessary. 

In good engines of that system the pressure in the condenser is 
usually 1*5 lb. per square inch, but the pressure in the cylinder itself, 
and under the piston, is in general 2-5 lbs. more, which gives p=4 
X144lbs. It has been deduced, moreover, from a great number of 
trials made on Watt's engines, that their friction, when working with 
a moderate load, varies from 2-5 lbs. per square inch of the piston, in 
engines of smaller dimensions, to 1*5 lb. in the more powerful ones ; 
which includes the friction of the parts of the machinery and the force 
necessary for the action of the feeding and discharging pumps, &c. 
By moderate load in these engines is meant about 8 lbs. per square 
inch of the piston. Now, our experiments on locomotives, showing 
the additional friction of an engineto be f of the resistance, give room 
to think that the additional friction caused in the engine by that load 
may be about 1 lb. per square inch. The above information attributes 
then to Watt's engines, working unloaded, a friction of from 1*5 lb. 
to # 51b. per square inch, according to their dimensions, which would 
give 1 lb. for engines of a medium size : this information, agreeing 
with what we have deduced from our inquires on locomotives, as has 
been said above, we shall continue to admit, in this place, respecting 
the friction, the data already indicated in this respect, viz. : — 
/= 1 X 144 lbs. 6 =-U. 

As an application of these formulae, we will submit to calculation 
£tn engine constructed by Watt at the Albion JWills near London,. 
The following were its dimensions : — 

Diameter of the cylinder, 34 inches, or ar=6'287 square feet ; 

Stroke of the piston 8 feet, or L = 8 feet; 
. Clearance of the cylinder, T / - of the stroke, or c=-4 foot; 

Effective vaporization, -927 cubic foot of water per minute, or S= 
•927 cubic foot ; 

Consumption of coal in the same time, 6*71 lbs. or N=6'7] lbs. ; 

Pressure in the boiler, 16-5 lbs. per square inch, or P=^16-5 X144 
lbs. ; 



321 

Mean pressure of condensation, 4 lbs. per square inch, or p=4x 144 
lbs. 

And finally, the engine being a condensing one, we have n=-4227 
and (j := -000000258. 

The engine had been constructed to work at the velocity of 256 
Feet per minute, which was considered its normal velocity ; but when 
put to trial by Watt himself, shortly after its construction, it assumed, 
in performing its regular work, esteemed 50 horse-power, the velocity 
of 286 feet per minute, consuming at the same time the quantity of 
water and fuel which we have just reported. 

If then we seek the effects it was capable of producing at its velo- 
city of maximum effect, and then at those of 256 and 2S6 feet per 
minute, we shall find, by the formulae already exposed : 





Maximum useful effect. 


v = 


286 


256 


v' =. 214 Velocity of the piston 
in feet per minute ; 


ar — 


5,621 


6,850 


9,133 Total load of the pis- 
ton in lbs. ; 


r 
144 

S = 


6-21 
•927 


7-57 
•927 


10*09 Load of the piston in 
lbs. per square inch ; 

•927 Vaporization in cubic 
feet of water per 
minute ; 



»-E = 1,607,610 1,753,600 1,957,180 Useful effect in lbs. 

raised to one foot 
per minute. 

"•HP = 49 53 59 Useful effect in horse 

power. 

a-EHb-co. _ 239,585 261,340 291,680 Useful effect of 1 lb. 

of coal, in lbs. raised 
to one foot per mi- 
nute. 

u-Eipe. =1,734,200 1,891,700 2,111,300 Useful effect due to 

the vaporization of 
one cubic foot of 
water, in lbs. raised 
to one foot per mi- 
nute. 

41 



322 

q co. for ih. - -138 -126 -113 Quantity of coal in 

lbs., producing the 
effect of one horse 
power. 

Qwa.forih. _ . 019 .Qi7 -016 Quantity of water, in 

cubic feet, produc- 
* ing the effect of one 

horse power. 

Such are the effects that thi3 engine should produce, and we se, 
in consequence, that in performing a labour estimated at fifty horses, 
it was to be expected the engine would acquire the velocity which in 
fact it did, viz., that of 256 feet per minute. 

Let us now see to what results we should have been led, had we 
applied the ordinary calculations to the experiment of Watt, which 
we have just reported. In this experiment, the engine vaporizing 
•927 cubic foot of water, and exerting the force of fifty horses, as- 
sumed a velocity of 286 feet per minute. 

We then find that, since the engine had a useful effect of no more 
than fifty horses, and that the theoretical force, calculated according 
to that method, from the area of the cylinder, the effective pressure in 
the boiler, and the velocity of the piston, was, 
6-287 X (16-5 — 4) X 144 X 286 
3^0 = 9S h0rseS ' 

It resulted that, to pass from the theoretical effects to the practical, 
it was necessary to use the coefficient -51. Consequently, by fol- 
lowing the reasonings of that theory, the following conclusions were 
to be drawn : — 

1°. The observed velocity being 2S6 feet per minute, the vapori- 
zation calculated on the quantity of water, which reduced to steam at 
the pressure of the boiler, might occupy the volume described by the 
piston, and afterwards divided, as is done, by the coefficient, to take 
the losses into account, would have been : 

■-^Vo X 6-287 X 286 
_ . — 2-305 cubic feet per minute, instead of -927. 

2°. The engine having vaporized only -927 cubic foot of water 
per minute, the velocity calculated on the volume of steam formed, at 
the pressure of the boiler, and afterwards reduced by the coefficient, 
not as has been done, since this problem was not resolved, but as 
must naturally be concluded from the signification attributed to that 



323 

1530 X '927 

coefficient, could but be ■ X '51 = 115 per minute, m- 

b'2o7 

stead of 286. 

3°. The coefficient found by the comparison of the theoretical ef- 
fects to the practical being -51, the various frictions, losses, and re- 
sistances of the engine would amount to -49 of the effective power ; 
whereas these frictions, losses, and resistances, consisting merely of 
the friction of the engine and the clearance of the cylinder, could be 
estimated only as follows : — 

Total friction (including the additional friction) 2 lbs. per 
square inch, or as a fraction of the effectual pres- 
sure, ^ -17 

Clearance of the cylinder, ± of the effective force, or . . -05 

•22 
Some authors also employ constant coefficients, not however using 
the same to determine the vaporization as to find the useful effect. 
This manner of calculating has arisen from those authors having 
recognised from experience, that the steam has in the cylinder a less 
pressure and density than in the boiler ; but as they cannot settle d 
priori what is that pressure in the cylinder, and that they always seek 
to deduce it from that of the boiler, instead of concluding it directly 
and in principle, from the resistance on the piston, as we do ; the 
diminution of pressure observed by them could not be defined in its 
limits, and it remained simply a practical fact which they used to ex- 
plain the coefficient. This change in the coefficient employed, avoids 
the first and second of the contradictions we have just indicated ; but 
the third, as well as all the objections we have developed in the first 
part against the use of any constant coefficient, remain in full force ; 
that is to say, that in this method, the power of the engine is calcu- 
lated independently of the vaporizing force of the boiler, and the va- 
porization independently of the resistance to be moved ; that the ef- 
fort exerted by the machine is found always the same at all velocities ; 
that no account can be taken of the opening of the regulator, unless 
a new series of coefficients be introduced to that end, as well as for all 
the changes of velocity, &c. 

In consequence, we conclude from this comparison, as well as 
from what precedes, that the theory in general use for calculating the 
effects or the proportions of steam-engines, cannot lead to any sure 



s 



324 



results ; while the one, which we have deducted from the best known 
principles in mechanics, and from the direct observation of what takes 
place in the engines, represents their effects with accurancy. 






325 



HASWELL'S VALVE 

FOR 

INJECTION, BLOW-OFF, AND DISCHARGE-PIPES 

OP 

STEAM VESSELS. 



In the body of the work, a valve invented by Mr. Haswell, of the 
United States Steam-frigate Fulton, has been referred to. A draught 
and description has, since that part was printed, been furnished by 
that gentleman. It is intended to be applied to the injection, blow- 
off, and delivering-pipes in steam vessels, for the purpose of cutting 
off at pleasure all communication between them and the water in 
which the vessel floats. These pipes may, in consequence, be re- 
moved and repaired without the necessity of going into dock ; and 
the vessel may be prevented from being filled with water, should they 
be injured by violence or burst by the frost. 



The annexed Fig. 1. represents a half-breadth plan, and Fig. 2. a 
vertical section of the valve and fixtures, as applied to an injection 
pipe. 

Note. When applied to blow-off pipes, one valve will answer for 
any number of boilers, by giving the top of the valve chamber a coni- 
cal or hemispherical form, with flanges for the connecting of branch 
pipes from the different boilers. 



326 



DESCRIPTION OF PLATE. 
Fig. 1. 

A, Opening through the bottom or side of the vessel. 
a, Lead pipe to shield the opening. 

B, Oak planking, to which the valve is first fitted and bolted, 
and then firmly secured to the shin of the vessel by the copper 
screws b. 

C, C, C, Valve chamber, of brass. 

D, Valve, sliding in grooves z, planed in the sides of the cham- 
ber. 

d, Valve stem, of copper. 

e, Stuffing box, for valve stem. 

f, Coupling, connecting valve stem and iron screw g, by which 
the valve is thrown forward to close the opening, or drawn back to 
admit of the water flowing through it. 

h, Standard and Binder, in which is placed the nut i. 

K, The Pipe, secured to the valve chamber by the Flange I. 

m, A Thumb screw, by which, when the valve closes the pipe, 
the water is drawn off in cold weather, to prevent its freezing and 
bursting the pipe. 

Scale. Three inches to a foot. 



327 



Kff. 1. 



Kff. 2. 






O 



o 



o 



o 



l .jr. 



m 



Fief. 6\ 



5\i 



v: 



Fig.5. [| 









-_ 



Jg 



,— jJ I 1 — , 



((";*.- 






ma 




_ o 


3 & f 






~— •-' ' ' — — ■ ' — ' 



Pz, .u . 



fiq. ff. 



Fig. 





If 



Fia'2 




t r 



I t 




■Li Jl" 






i 




- 1 fe, 



«<?2 




r 




Pl .r. 




PioFF 




/'/..] / 







Pl .irzr 




1 ' .. 





5; : aii::*iG^ 






Scale . £ to the foot 






\) 619 



ti/ 



LIBRARY OF CONGRESS 



021 213 136 2 



HP 



» 



HI 



I 







iff 

in 



Mil 



